Compatibility update

[tanxpyox]

Main changes:

1. Adds arguments to extractFeatures and extractFeature to suppress inclusion of raw_data and timestamps in the output feature matrices. Suppression is on by default.
2. Features are matrices instead of data frames to allow smoother integration with hmm.
3. Adds an argument standardize to extractFeatures. When true, it standardizes the feature matrices before output. (Note: standardizeFeatures is not an exported method.)
4. Moves raw_data and timestamps to root to avoid compatibility issues with functions that only take features as matrices or lists of matrices
5. Adds a $file attribute to the extractFeatures output for easy access of metadata. Currently contains:
   • $fname: vector of filenames corresponding to the sources of the feature matrices
   • $duration: vector containing the row numbers of the feature matrices - for assigning fold in cross-validation model training.

Misc changes:

1. Updates hmm.R and llh.R so that they work for matrices created after R 4.0.0
2. Export llh() so that it can be used to evaluate model performance.
3. hmm.R: when called with verbose = 0, stdout messages from standardizeFeatures (when standardize = T) and 'failure to converge by max iter' warnings are suppressed.