Renaming a couple of poorly named player OST's

*Change the vague and indescriptive OST equates "layer" and "layer_plus"
to the more accurate and decriptive (and accurate) "top_solid_bit", and
"lrb_solid_bit", as named in the Sonic 3k disassembly, which also
removes repetition of the word "layer".
*Changed the RAM constants to "Saved_layer" and "Saved_layer_2P" to have
the more fitting names "Saved_Solid_bits" and "Saved_Solid_bits_2P".
Merge pull request #2 from Caverns4/Layer-OST-Renaming

Renaming a couple of poorly named player OST's