Build with latest version of MPIDE using upstream Arduino-Makefile.

May fix #139.
Remove duplicate clean target for pic32.
Remove duplicate includes, causing errors with latest MPIDE.
Update flags and paths for latest Arduino-Makefile.
Use updated flags for extra C/C++ flags in Arduino-Makefile.
Use updated flag for debug baud on pic32.
Install ISR on PIC32 with updated build script.
Restore 'clean' target for all platforms.
Disable NETWORK option - not working with latest MPIDE.

See #189.
Update docs for new MPIDE build.