evolvestate: add a class to wrap the state of `hg evolve` command This patch adds a new file which contains a class which will act as a wrapper for the data to be stored or used during the `hg evolve` command. This patch just introduces the file and does not use it at the moment. The upcoming patches will start using it.

. $TESTDIR/testlib/pythonpath.sh

cat >> $HGRCPATH << EOF
[extensions]
docgraph=
EOF