Write script to port mastersnippets to reworked format

[jhakala]

Before merging #211, we will need a script to port the existing mastersnippets into the new format. Another feature to automatically update cfgcvs would also be useful, but it should be kept separate, to support generating updated mastersnippets without touching cfgcvs.

[kakwok]

Mostly done in #211, but needs more testings on P5 masters and handles the single v.s. multi FM parameters