Merge pull request #1 from tgulacsi/chunked

add chunked decoding and test for it
add extra (_) fields implementation
writer: expand getCaller test coverage
writer: simplify MarshalJSON + test extra fields roundtrip
writer: remove testing values from m.Extra in Writer.Write()
writer: remove debugging panic
doc: README: update todos
Merge remote-tracking branch 'upstream/master'
Merge pull request #3 from lethain/extrafields

Extrafields
merge (replace ours with theirs) upstream