minor tuning on threshold and default ppm setting

now aligned with matlab. there is difference from peak calcellation s…

…trategy in peak_search()

Update README

try matlab native viterbi decoder. and shrink x-rnti from 0~3D to 1~3C

change pdcch_bit_level_proc to detect num_bits smartly

update

update README

prepare to release

ready for release now

done with TDD, external LNB, and faster pre-search