v0.2.15

Added

• Padding modifiers %_?, %-? and %0? are implemented.
  They are glibc extensions which seem to be reasonably widespread (e.g. Ruby).

• Added %:z specifier and corresponding formatting items which is essentially the same as %z but with a colon.

• Added a new specifier %.f which precision adapts from the input.
  This was added as a response to the UX problems in the original nanosecond specifier %f.

Fixed

• Numeric::Timestamp specifier (%s) was ignoring the time zone offset when provided.

• Improved the documentation and associated tests for strftime.