ChangeLog: Document changes since v0.4.0
ChangeLog: Document changes since v0.4.0

Through 6734c7a (Merge pull request #370 from
vbatts/json_schema_and_examples, 2016-04-11).

The only unlisted changes to master were a brief run with ffjson
(#343, #351), but that was pulled out due to gccgo issues in #363.

Signed-off-by: W. Trevor King <f75897670c17327c42ab201733fb8a81ff9f4c34@tremily.us>

opencontainers/runtime-spec,vbatts/specs,laijs/specs,wking/opencontainer-specs,cloudfoundry-incubator/specs,ujuc/specs,jonboulle/specs,hqhq/specs,opencontainers/specs,wking/opencontainer-runtime-spec,hqhq/runtime-spec