Issue #520 Shutdown Heka on SandboxDecoder failure
* invoke drainChannels prior to exiting from ManagedCmd::Wait()
* ManagedCmd timeout is just a special case of Stopping now to prevent goroutine leaks
* CommandChain was leaking goroutines on subcommand error. Chains now
  report a single aggregate error to prevent goroutine leaks.
Issue #525 remove top level 'table' element from Lua sandbox JSON serialization

- Documentation update.  Starting a 'cookbook' of common sandbox use case examples
Merge pull request #521 from Seldaek/patch-1

Docs consistency fixes for ProcessInput
Merge pull request #523 from Seldaek/severity_docs

Improve severity docs
Merge pull request #524 from mozilla-services/issue_520

Issue #520 Shutdown Heka on SandboxDecoder failure
Merge pull request #526 from mozilla-services/features/505-processinput-fixes

CommandChain and ManagedCmd fixes to prevent goroutine leakage
Issue #525 Remove comment
Merge pull request #527 from mozilla-services/issue_525

Issue #525 remove top level 'table' element from Lua sandbox JSON serial...
Add 0.4.1 release date.
Use 0.4.1 tag for heka-mozsvc-plugins.
Merge branch 'versions/0.4' into dev

Conflicts:
	CHANGES.txt
	cmake/externals.cmake
fixes #535 and re-enables the DecoderSpec
Remove client's JsonEncoder since we removed the JsonDecoder a
while back.
Merge pull request #536 from mozilla-services/features/535-enable-decoderspec

fixes #535 and re-enables the DecoderSpec
And toml refs.
Merge pull request #537 from mozilla-services/remove-json-encoder

Remove client's JsonEncoder
Make it possible to return (nil, nil) in Decoder.Decode
Add log_errors flag to the PayloadRegexDecoder, fixes #279
Update docs