GDB pretty printers

[heinezen]

Introduces custom GDB pretty printers. These will make fixed-point values, that were previously very hard to parse, human-readable:

• curve::Keyframe
• time::time_t

(gdb) p current_time
$1 = 2.593s = {raw_value = 169934}

• util::FixedPoint

(gdb) p fp
$1 = 1.16888 = {raw_value = 76604, approx_precision = 5}

• util::Vector