dialyzer fixes, changed newentry callback
Incompatible change to setopts

The setopts callback for probes was made asynchronous, and passes
the args (#exometer_entry{}, Options, NewStatus). A new module,
exometer_info.erl exports accessor functions (exprecs-style) to
facilitate access to record attributes without compile-time deps.

The reporter_setopts callback now receives the #exometer_entry{}
record again, since race conditions could result from fetching
it in the reporter process.
added functions + docs in exometer_info
Merge pull request #90 from Feuerlabs/uw-dialyzer-fixes

dialyzer fixes, changed newentry callback
fix doc on exometer_entry setopts callback
regenerated docs
added bounded highnum retention for histograms
fixed docs on starting exometer
make highest values follow sliding window
Merge branch 'uw-histogram-accuracy'
Fix template + option processing semantics

- When creating a new entry redefining a default definition, options
  replace default options with the same key.
- The special option {'--', Keys} removes given option keys from the
  default specification.
- Added 'sys' message handling to exometer_proc, which means that
  `sys:get_status(exometer:info(Probe, ref))` will work.
Initial opentsdb support
Fixing typo
Few bug fixes
Doc update
Doc
Merge pull request #93 from Feuerlabs/uw-template-options

Fix template + option processing semantics
- added {truncate, round} as option to histograms
- added system message handling in exometer_proc
- removed exo from deps (not used)
- bug fix in exometer_folsom_monitor
- exometer_report:reporter_pids() return only valid pids
- fix corner case when fetching highest values for histogram
removing unused function
remove unused local function