- use volatile for registers
- avoid implicit casts

I've just uploaded a major change to pinsDebug.
The big change was creating an array in FLASH that contained every
active pin definition. That reduced the RAM memory usage considerably
but increased the FLASH usage.
Creating the array requires going through the pin list twice. Rather
than having two copies of it in the code I moved the list out to another
file (pinsDebug_list.h) and then just did two #includes.
From the user’s view they’ll see the following changes:
1. Now reports all the names assigned to a pin
2. The port is now reported in addition to the pin number.
3. When PWM0A & PWM1C share a pin, both PWMs are reported
4. More PWM/Timer info is reported
One new item that may cause some concern is the usage of the LINE
predefined preprocessor macro. It may not be available if the Arduino
IDE goes to a different compiler.

Includes support for 1284 & 1286 families.

Memory usage changes when enabling PINS_DEBUGGING:
ATmega2560
FLASH
.           without   52576
.           with new  64592
.           with old  62826
.           new-out   12016
.           old-out   10250
.           new-old   1766
.
RAM
.           without   2807
.           with new  2875
.           with old  3545
.           new-out   68
.           old-out   738
.           new-old   -670

==================================================================

minor changes - mostly formatting

1) added newline to end of teensyduino file

2) changed flag name from TEENSYDUINO to TEENSYDUINO_IDE.  Got warnings
about redefining TEENSYDUINO

3) removed some trailing spaces

reduce PROGMEM size & update pin list

Reduced PROGMEM usage by
1) converting often used macro to a function
2) moved as much as possible into the function

This required creating two arrays of address pointers for the PWM
registers.

==================================================================

update with new M3, M4, M5 pin names

==================================================================

report I/O status for unused/unknown pins

I've just uploaded a major change to pinsDebug.
The big change was creating an array in FLASH that contained every
active pin definition. That reduced the RAM memory usage considerably
but increased the FLASH usage.
Creating the array requires going through the pin list twice. Rather
than having two copies of it in the code I moved the list out to another
file (pinsDebug_list.h) and then just did two #includes.
From the user’s view they’ll see the following changes:
1. Now reports all the names assigned to a pin
2. The port is now reported in addition to the pin number.
3. When PWM0A & PWM1C share a pin, both PWMs are reported
4. More PWM/Timer info is reported
One new item that may cause some concern is the usage of the LINE
predefined preprocessor macro. It may not be available if the Arduino
IDE goes to a different compiler.

Includes support for 1284 & 1286 families.

Memory usage changes when enabling PINS_DEBUGGING:
ATmega2560
FLASH
.           without   52576
.           with new  64592
.           with old  62826
.           new-out   12016
.           old-out   10250
.           new-old   1766
.
RAM
.           without   2807
.           with new  2875
.           with old  3545
.           new-out   68
.           old-out   738
.           new-old   -670

==================================================================

minor changes - mostly formatting

1) added newline to end of teensyduino file

2) changed flag name from TEENSYDUINO to TEENSYDUINO_IDE.  Got warnings
about redefining TEENSYDUINO

3) removed some trailing spaces

reduce PROGMEM size & update pin list

Reduced PROGMEM usage by
1) converting often used macro to a function
2) moved as much as possible into the function

This required creating two arrays of address pointers for the PWM
registers.

==================================================================

update with new M3, M4, M5 pin names

==================================================================

report I/O status for unused/unknown pins

added conditional compilation for PWMs 1C & 3C

add Teensyduino compatibility

==========================================

changes per review - minor formatting changes

1) remove non-printable character at the end of line 687

2) split a really long comment into two lines

3) got rid of some trailing spaces

============================================

Made pinsDebug_Teensyduino.h the same between this PR and PR 5668 which
is for a re-written pinsDebug.h file.

The changes were:
1) added copyright @ GNU license header
2) a blank line crept in.

Unlike RAM-based strings, PROGMEM strings aren’t consolidated by the
compiler.

・Add CASE_LIGHT_PIN into pinsDebug.h

see detailed  description in PR #5118

I stumbled across a name change that'll be used a lot so I'm updateing
the name list.