fix handlers_in_progress_count in mutators
log failed extension mutator name instead of empty curly braces
Update regex to allow periods in check names

* regex will allow periods anywhere but the beginning of the check name
* verified with http://rubular.com/r/bgptLyK6F4
Merge pull request #556 from skymob/allow_periods_in_check_names

Update verify_check regex to allow periods in check names
client & check names cannot contain spaces or special characters
       support: a-z A-Z 0-9 _ . -
Merge pull request #557 from portertech/definition-names

client & check names cannot contain spaces or special characters
[docs] added sensu docs to readme
[docs] updated the changelog, 0.10.0 TBD
Merge pull request #558 from portertech/docs

updated readme (docs link) & changelog (0.10.0 TBD)
[exited] fixed sensu popen nil exit status
Merge pull request #559 from portertech/exited

Fixed sensu popen nil exit status
Merge pull request #554 from piavlo/bug/handlers_in_progress_count

fix handlers_in_progress_count in mutators
[extension] use mutator extension definition in error messages
Merge pull request #561 from portertech/extension

[extension] use mutator extension definition in error messages
[valid_payload] removed result validation, determined case of nil exit status
[valid_payload] trust the message bus
Merge pull request #562 from portertech/valid_payload

Trust the message bus
[debug_handler] stop double json encoding event data
Merge pull request #563 from portertech/debug_handler

[debug_handler] stop double json encoding event data
[redact] redact passwords in client data