fixed markdown rendering issue (literal '<' are interpreted)
Merge branch 'master' into igalDruid
Merge branch 'master' into igalDruid
syntax and grammar fixes; tightened up language and flow
Fixed:

- Bad link for granularitySpec changed to real definition.
- All heads set to logical levels (consistent with all others).
- Fixed bad link in definition for spatialDimensions.
Merge branch 'master' into igalDruid
Merge pull request #432 from metamx/igalDruid

Igal druid