Uart glitching improvements

[mbrugman67]

This closes issue #196

A few changes to the glitcher to:

• increase resolution from 1 microsecond to 10 nanosends: changed clock divider in PIO state machine, removed magic multiplier from FIFO to SM
• renamed setup_hardware() and teardown_hardware() methods to setup_uart_glitch_hardware() and teardown_uart_glitch_hardware() respectively. The original generic names would doubtlessly resulted in a collision at some point in the future
• clean up some wrong/misleading comments
• fix loop counter variable datatype (from uint8_t to size_t)

The timing seems correct with test equipment I have.