Allow setting the number of bases at read start that should should be ignored for conversion statistics

[vinjana]

According to this article the biased region during PBAT may extend further than 9 base pairs. However, the current script only ignores 9 bps when creating conversion statistics.

• Make the number of bases to be ignored configurable, including the value 0 (=ignore no base) and values larger than 9.
• Keep only the new version of the script while removing the original methylCtools script.
• Make a pull request for methylCtools.