Added usage description for per-directory config.
Added custom UTC tzinfo.

See 96e63168a6e78beb4683b26235d8db02547eea6f.
Bring back custom datetime parsing/formatting.

This reverts 96e63168a6e78beb4683b26235d8db02547eea6f.
Bring back custom delta parsing/formatting.

This is based on the code removed in 437d628c46f5a0fbbf819a9e898e1fe8637298a4,
but supports microseconds for round-tripping output produced while isodate was
in use.
Remove isodate from requirements.
Added usage description for per-directory config.
Merge branch 'feat/remove_isodate'

Closes #8.

* feat/remove_isodate:
  Remove isodate from requirements.
  Bring back custom delta parsing/formatting.
  Bring back custom datetime parsing/formatting.
  Added custom UTC tzinfo.
  Added usage description for per-directory config.
0.11.0 released.