PositionalMTFEncoder

[GaurangTandon]

Description

• Takes a buffer, bwt pointers into that buffer, and a boolean array of used bytes
• Converts the (used) bytes to their respective positions (0..count_bytes)
• Then applies MTF on these bytes

Tests

• [x] distinct bytes small
• [x] repeating bytes small
• [x] repeating bytes large

[GaurangTandon]

1. I'll remove the println!'s on the next commit (forgot earlier :P)
2. Considering the tight coupling with ptr and in_use, should we move this directly to encoder module itself, instead of keeping it in standalone move_to_front.rs?
3. Any other comments on performance code or otherwise? (I left a couple of TODOs as I couldn't figure them out yet, if you know, please tell :D)

[GaurangTandon]

For future reference:

MTF generator code
Random string generator