Fix to filter empty room before calculating cov.
jumeg_filter minor changes
Simpler way to construct filename.
Include option to filter empty room files.
Minor filename fix and cosmits.
Merge pull request #38 from pravsripad/empty_room_filt

Fix to filter empty room before calculating cov. The application of filter is optional. Empty room files are saved as '-empty.fif' and covariance files as '-cov.fif'. Empty room cov matrices are saved as '...,empty-cov.fif'.
Merge pull request #39 from fboers/fb_filter-mne-bw-ws-001

jumeg_filter minor changes