Fixes a bug I introduced with SSL for testing
Print Error()
Merge pull request #613 from freeformz/benchmark_error_formatting

Print Error()

[skip ci]
Merge pull request #612 from freeformz/fix_benchmark_mistake

Fixes a bug I introduced with SSL for testing

[skip ci]
Fix #608. Fix merge when one of the series doesn't yield any points
Cleanup (Thanks, @freeformz)

Close #618. Close #617. Close #616. Close #615. Close #614
Add having clause.

you can query having clause like this.

   select mean(cpu), host from service group by time(1m), host having top(mean, 10) and host = 'service1'

Having Clause Syntax:

   group by columns [having CONDITIONS]

* having clause supports top and bottom. other aggregate function doesn't support.
  * you can't call top and bottom multiple times.
  e.g) having top(a, 10), bottom(b, 10) could not evaluate
improve filter.
use series.Fileds
remove having engine. it should process QueryEngine
improve having clause setup. and fix having limit
remove needless log
add parser test
check memory leak when parsing having clause
prevent panic when having result is null
adjust blank line
don't check condition twice
prevent panic
add more test cases