extract_features: Creates a dictionary (dataframe) of all features in the data
In NLeSC/EEG-epilepsy-diagnosis: Epilepsy detection with emotiv data

Extracts features from raw EEG data using wavelets

1	extract_features(cleandatadir,filtertypes,epochlength,fn,sf=128,n.levels=7)

`cleandatadir`	location of the csv-files with cleaned data per person
`filtertypes`	wavelet filter types as expected by the mra function from the wavelets package, e.g. c("d2","d4")
`epochlength`	duration of epoch (time window) in seconds
`fn`	names of features to extract from wavelets, e.g. "sd" to extract the standardard. Underlying code includes explorative work on other features
`sf`	sample frequency in Hertz
`n.levels`	number of wavelet levels to extract