added a directory structure for the project. data files (and maybe figure) will not be shared via git. they'll have to be shared by explicit copying. added an initial draft of the derivation of the Poisson-Binomial model for TF-specific DNase footprint. added scripts implementing the different versions of the Poisson-Binomial model for TF-specific DNase footprint. Dervied Centipede with Poisson-Binomial model. completed modifications to document and code for Centipede-PBM. fixed compile bugs in centipede_pbm. added a wrapper script. streamlined the code a bit more.