TTSServices are now providers of TTSEngines + log file

- It is then possible to pass runtime options from the config file to engines
- the log feature fixes #19 (for the most part)
- The TTSEngines are tested in the ssml-to-audio step, rather than inside the engines
- Changed SAPI's SSML adapter to remove the ssml:tokens
- Added SAPI's SSML XSLT adapter to the artifact resources
- Acapela's library loading is performed earlier to make it easy to catch exceptions
- OSX TTS can use different voices
- Acapela's servers are no longer tested individually (regression)
- ATT engine is temporarily not supported (regression)
Moved mark handling from TTSService to TTSEngine

- SAPI mark handling can now be disable/enable via the config file
- Use audioFormat.match instead of audioFormat.equals everywhere
Merge pull request #29

Close #29
Voices now belong to an 'engine' rather than a 'vendor'

- SAPI's engine is now always 'sapi'
- No longer possible to provide the sames voices with different engines
- This somehow resolves #27, since we don't need to share voices anymore
- Fixes a bug in SAPI regarding the mark handling switch
Minor changes

- Removed @xml:lang from the SSML provided to SAPI
- Never pass a null list of marks to the TTS engine
- Catch more exceptions
Merge pull request #33 from branch 'vendor-semantic'

Close #33
Write TTS logs in the output directory

- Not backward-compatible
- Must be synchronized with pipeline-script's logs-in-output-dir branch
- Only available for DTBooks, for now;
- Lightweight version of the Log object when the logs are disable.