minimodem: free samplebuf to appease valgrind
fsk: calc separate divergences for mark and space bits

Calculate and consider separate signal-strength divergence values for
mark and space bits, so that imbalanced (but consistent) mark/space
strengths do not drive down confidence.

Note: This change makes all existing test cases yield very slightly
higher confidence values.
Add option to change start-stop polarity
Change code to use 64-bit variables for decoding
Add Windows executable to gitignore
Compute expected bit strings outside of main loop
build_expect_bits_string cleanup
Really use 64 data types for demodulation

[ kamal: cleanup ]
Add UIC-751-3 decoding and optional MSB-first TX/RX

[ kamal: cleanup ]
Honor --invert-start-stop in TX
minimodem: accept "uic*" for uic-ground
add Marcos Vives Del Sol to AUTHORS and debian/copyright
man: add uic-train and uic-ground modes