Merge tag '0.1.11' into develop

Release 0.1.11

b88da0fd (HEAD -> master) Merge branch 'release/0.1.11'
eec6773f (release/0.1.11) version bump
d07a1490 (develop) dependency bump
2bcf9783 (origin/develop) [tx builder] allow to set expiration from outside
a060565a Merge branch 'SmileyChris-master' into develop
8cd8d76d (origin/SmileyChris-master, SmileyChris-master) Merge branch 'master' of git://github.com/SmileyChris/python-bitshares into SmileyChris-master
26fa540c [message] improvments to message parsing
a1cd2ef2 bump dependency version
b16d82fc [blockchain] fix 'stop' parameter in blocks()
223b2748 [docs] fix intendation errors when building docs
b46cd148 [docs] add worker.rst
24903b5b [tests] fix test case for asset_issue
4008070d [memo] improve interface of bitshares.memo
03707966 [memo] simplify the use of bitshares.memo
3137f8b1 bump dependency on python-graphene
00549ced [operations] asset_* operations
118a55fa Comment about the magic `mocker` argument
5f0f8068 cleanup makefile
c3c4579c Merge tag '0.1.10' into develop
8096f75d Add basic test for Asset.calls property
c
ea86ad Fix method call in Asset.calls property