Allows position RangedData argument to have multiple spaces.
Introduces argument checking.
Adds `na.rm = TRUE` to peptide summarization methods, in case of removed
spots. 
Uses the match function to match peptides in peptideSet with rownames of
RangedData position object.
Merge branch 'master' of ssh://git@github.com/RGLab/pepStat.git
Imports cbind method from IRanges package