Add additional normalisation method?

[connorrogerson]

This is not an issue, but a suggestion of an additional normalisation option. I've been processing from iCLIP data recently, and the normalisation there seems to be a signal-background-ratio, where a bin is ratioed by the two adjacent bins on either side (this controls for local signal). This could be done when performing bamCoverage if the smooth-length option could be edited to ratio rather than average. Just a suggestion and if anyone has any suggestion on how to perform the normalisation, let me know!