more docs tweaks [ci skip]

bump version to v0.13.0 and fill in the changelog and the upgrade docs

update the changelog and bump the version to v0.12.0

version bump

version bump (forgot to do it with v0.10.8 release, so have to go for…

… v0.10.9)

update the changelog with everything we've added in v0.10.8

Fix changelog

Bump to v0.10.6

Merge branch 'fix-reloading-strict' of https://github.com/paularmand/…

…mongoengine into fix-reloading-strict and bumped version.

# Conflicts:
#	AUTHORS

Merge pull request MongoEngine#1167 from BeardedSteve/upsert_one

Upsert one