* Prom exporter structure
* update prometheus exporter with master and add example.
* remove distributedcontext from prometheus example
* docs and interface checker
* make precommit
* make precommit & remove "OnRegisterError"
* coerce values to float
* return register errors and maybe fix precommit?
* add option to specify a prometheus.Registry
* make exporter implement http.Handler interface
* fix map keys bugs
* remove unused const
* fix modules dependencies.
* add support for histogram
* get metrics with labels values only instead of a labels map
* make exporter implements label encoder interface
* encode labels if the encoder is different.
* split metrics on several files and encapsulate them in structs
* make pre commit
* unexport 'sanitize'
* remove 'AllValues' in favor of 'Points' and change to 'NewDefaultLabelEncoder'
* add prometheus tests
* remove newlines on struct declaration
* formatting
* rewording
* imports
* add todo on labelValues
* blame myself for todo (:
* add todos on sanitize
* add support for summaries. custom remove label encoder.
* imports
* imports
* update with upstream
