avoiding duplicate rebuilds of the same image, and also
allow personal docker hub repositories for private fork
builds to be optimized. Move ubsan build to artful image
because it catches more stuff and fix what was found.
THRIFT-4345: solidify docker build strategy for maximum
coverage: trusty, xenial, artful as stock as they can be
THRIFT-4344: add top level language summary markdown and
update readme with a new image on the layered architecture
THRIFT-3847: remove VERSION macro from config.h which
was causing a conflict on artful builds.
THRIFT-4359: fix haxe map/set decode when key is binary,
as a missing break statement caused it to use an int
during decode
This closes#1389
