Remove TimeParser.

**Breaking change** (feature removal), so we'll need to up the version number to `0.2.0` in the next release.

* The 'seek' command no longer accepts units, and can only be instructed
in microseconds.
* TimeParser::MicrosecondPosition is now std::uint64_t.

Why am I proposing to remove this?
* Code simplicity;
* The only uses it has are in debug (other programs will always seek in microseconds), and
* We can use external front-ends to replicate the functionality.  For example, [baps3-cli] has a program `baps3-seek` that can be told to use hours/minutes/seconds/milliseconds.
* If not, then Google, `calc.exe` or `bc` has you covered (just multiply your intended unit out into its equivalent in micros before sending it) :grinning:

[baps3-cli]: https://github.com/CaptainHayashi/baps3-cli