RF: Change variable names
Merge pull request #12 from hoechenberger/variable-naming

RF: Change variable names
RF: Reworked statistics

The new ttest() function also supports groupby splitting of the input data.
Merge pull request #13 from hoechenberger/statistics

RF: Reworked statistics
RF: Rename get_cdf*() functions to get_percentiles*()
RF: Remove most of the DataFrame functions
RF: Add newlines
Merge remote-tracking branch 'origin/cdfs' into cdfs

Conflicts:
	pphelper/tests/test_racemodel.py
	pphelper/utils.py
RF: Add newline
Merge pull request #14 from hoechenberger/cdfs

Cleanup naming, remove some DataFrame functions
RF: Move get_max_from_list() test to test_utils.py
NF: Add sum_cdfs()
RF: Rename variable
Merge pull request #15 from hoechenberger/sum-cdfs

NF: Add sum_cdfs()
DOC: Update docstrings
Merge pull request #16 from hoechenberger/doc

DOC: Update docstrings
NF/RF: Add back gen_cdfs_from_dataframe(), completely reworked
Merge pull request #17 from hoechenberger/df

NF/RF: Add back gen_cdfs_from_dataframe(), completely reworked
NF: gen_cdf() removes negative RTs

Negative response times are removed before constructing the empirical CDF. In this case, a warning is issued..
NF: gen_cdfs_from_list() can now return a list of Series