improve histogram rendering in parse_session_stats.py and add some more graphs
improve histogram rendering in parse_session_stats.py and add some more graphs

git-svn-id: 51f496e7cf1b55ee487494d18ee2d308bae7fe77@6014 f43f7eb3-cfe1-5f9d-1b5f-e45aa6702bda

steeve/libtorrent,steeve/libtorrent,steeve/libtorrent,steeve/libtorrent,steeve/libtorrent,steeve/libtorrent