Reworked voice parsing and mapping

With new regular expression pattern, captures all voice output fields,
using the file name as the "official" voice name that is passed back to
the CLI. All other canonical names from the output are setup as aliases
that point to the "official" voice name (the file name).
Fix for Windows paths in eSpeak

Because Windows uses a different path separator, the regular expression
must adjust for that.
Variant support for eSpeak

Introduces support for variants with eSpeak using the 'voice+variant'
syntax to the CLI.
eSpeak documentation update

Adds information about variant and updates the screenshot.
Merge branch 'chg/espeak-46' into develop

Adds support for variants, fixes Mandarin support, and improves parsing
for the eSpeak service.

Fixes #46.