Added 2 bytes USB config data for Bootloader feature flags and application version

• New micronucleus bootloader and binary version 2.6 with info function.
• First version without MH-ET LIVE Tiny88(16.0MHz) support, since it is now supported by ATTinyCore.

New micronucleus binaries for all platforms

• New micronucleus binaries for all platforms.
• Bootloaders with updated MCUSR handling.
• Updated examples and added warnings for CDC examples.

Support of the cheap Chinese MH-ET LIVE Tiny88

• Support of the cheap Chinese MH-ET LIVE Tiny88(16.0MHz) board with ATTinyCore.
• Corrected wrong mouse buttons PR#2.
• Updated boards.txt to make use of menus. Therefore some board names changed like digispark-tiny1 -> digispark-tiny:clock=clock1 etc.
• Set OSCCAL to factory default instead of using a rule of thumb, which was not reliable.
• Added linker flag -mrelax. This reduces code size at least for ATtiny167.