Rename variables with obscure names.

The `snr' variable has a very obscure name. Rename it to `matchWeight'.
Also, the `toLowerCase' function is error-prone, since it actually returns
a lower case version of the BASE char, that is without diacritics. Hence,
rename it to `toBaseLowerCase' and update variables with similar names.

Change-Id: Ibdbe73018a33ee864db59a51d664c3b104d5fb3f