Glitcher uses clk_in instead of SysClk.
Implemented a FIFO for the glitcher; testbench.
External trigger support.
Added external reset, removed external enable.

- rst_o will take care of providing an active-low reset signal for the
  target.
- external enable pin removed and glitcher will now start reading the FIFO
  as soon as it reports that it's full.
- testbench updated.
FIFO support (width of 32bits, depth of 100)