improve ex_utils python module

We add these features:
- adjustable system frequency
- access to system clock object
- enable tracing
- enable gdb (only partially working)
add support for U2X bit in UART
add more subsystems to Python wrapper
try to avoid sending '\0' char when UART is enabled
change behavior of UART to match a real ATmega328
fix crash if name of trace file doesn't contain a dot
implement U2X bit for receiving in UART
optionally disable output to std::cerr in SerialTx

Conflicts:
	src/ui/serialtx.cpp
try to make gdb work better - doesn't help much
implement doRun and doStep in C to improve speed (3x in my case)
Merge pull request #1 from yeyus/jft_merging_bbb

merging bbb changes but fractional clock