Rockbox

This patch is a major rewrite of the mp3_encoder.
Bugfixes:
- avoid overflows in the granules' bit reservour at high bitrates
- correct bitorder for bit quadruples in huffman coding
- avoid compiler complaining in 'logf' compilations
- correctly use the encoder in viewer plugin mode (no double file selection)
Optimizations:
- use latest lame 3.97 windowing and mdct algorithms
- up to 5% better bit reservour usage by distributing overhang bits to remaining granules of current audio frame
- faster noise allocation
- better quality at low volume audio input (two path integer calculation)
- reduce screen updates
The patch gives better quality at low volume and high bit rate encodings at
40% increased speed with less IRAM usage.