organize the code for v0.2.1 into single directory so it will
be easy to track and deploy.

New fc_ovlp_to_graph.py replacing the falcon_asm_v2_dev.py.
It keeps all graph edge infomation in its output now.

A new class for reading the output from fc_ovlp_to_graph in fc_asm_graph

fc_ctg_link_analysis.py is a code as an example analyzing "missing
links" between contg.

fc_graph_to_contig.py replaces gen_contigs.py

a new python multi-processing base overlap filtering code replace
old script using parallel and 3 seperate python scripts
remove the file as it is replaced by fc_graph_to_contigs.py