Override complete compiler tool paths for chipKIT.

Previously we were setting the AVR tools path to the PIC32 tools path because it
made grabbing the compiling tools easier. Consequently, it made finding the
avrdude path much harder, especially since the avrdude files are in different
locations in the Linux distributions of MPIDE and Arduino.

Instead, we set the AVR tools path to the *correct* path (where *AVR* dude
lives), and totally override the CC, CXX, etc. paths to point to their PIC32
equivalents.
Silence the stderr output from call to `which`.
Don't hard code MONITOR_PORT in examples, for more flexible testing.
Use more reliable serial device naming in Windows.

* Strip leading "/dev/" from MONITOR_PORT before handing to avrdude in Windows.
* Use the more widely available awk tool instead of bc to subtract 1
    from COM ID (as opposed to `bc`).
* Allow Windows user to specify "com1" or just "1".
* Document MONITOR_PORT format for Windows users.
Document that ARDUINO_DIR must be a relative path in Windows.
Merge pull request #155 from peplin/monitor-port-check

Use more reliable serial device naming in Windows.
Document that ARDUINO_DIR must be a relative path in Windows

Fix #156
Merge pull request #157 from peplin/no-hardcoded-port-in-examples

Don't hard code MONITOR_PORT in examples, for more flexible testing.
Merge pull request #158 from peplin/silent-which

Silence the stderr output from call to `which`.
Merge pull request #159 from peplin/simpler-crossplatform-paths

Override complete compiler tool paths for chipKIT.
Update changelog about the recent changes
Update `README.md` about compatibility with Windows

Fix #94
Fix some typos and errors in changelog
Bump up version to v1.3.0 for release