Improvements to DIRHA and HTK interfacing modules

In interfaces.htk,

Added function to read HTK results

readhtkconfig now optionally translates HTK units (100ns) to samples.

writemlf writes MLF from a list (respecting order)
improved readmlf2dict and mlf_reg2key
readscp now returns None for source_paths when none provided

In interfaces.dirha,

Fixed regular expression for grid_dirha and included regexp for speech events.

Added microphone list, functions comp_* to compose dirha file paths from their
parameters and a function to fix truncated names in meta-data.

readmetadata now reads mic metadata and parses the entire pos field. Also added
functions that returns speech events in a dict or a list.