add more comments for bvgraph.h, bvgraphfun.h
add mainpage.dox for document
add more comments for source code
add offsets file
update Makefile
rm mainpage.dox
rm bv_line.offsets from test/ dir
rm bv_line.offsets in Makefile
Merge pull request #19 from yuyongyang800/bvgraph

Bvgraph with comments for generating docs