Plugins

[jacobpennington]

WARNING: Large / Dangerous pull request! Please allow time for testing by @svdavid and others before approving and merging.

Big rework for NEMS' xforms system, including changes to keyword formatting and implementing plugins for user-defined keywords.

Highlights:

• Modelname syntax has changed. See docs/keywords.md for examples.
• All LBHB-specific loader functions have been moved to nems_lbhb (inside nems_db)
• nems.keywords no longer exists! the default keywords now reside in nems.plugins.default_keywords.
• Default configurations are now in nems.configs.defaults.
• Users can specify their own loader, module, and fitter keywords to register with NEMS by pointing to their code in nems.configs.settings (using the KEYWORD_PLUGINS, XF_LOADER_PLUGINS, and XF_FITTER_PLUGINS options).

Minor changes that got mixed in:

• Started adding support for as_continous and other methods to signal subclasses - some models were not working without these changes.
• Reformatted the bounds parameter in coordinate_descent to agree with the changes to nems.fitters.mappers

[jacobpennington]

Note regarding the travis build failure: They are all passing on linux, but failing on mac due to part of the config code that creates an empty settings.py file when one does not exist. Working on a fix for this.

[svdavid]

@jacobpennington Travis seems to be failing for MAC OS X when it tries to load settings. It works fine on my MAC, so I'm a little confused. One thing I do see is that "settings.py" is created on my machine when I run pytest, even if it doesn't exist before I run it. So I think it's ok. Would be nice to merge. Maybe @bburan has thoughts on the best way forward?