Fixes:

  * Fix observations count
  * Fix NilComparison exception

Changes:

  * Return nil for queries if no observations are available
  * Make Quantile objects comparable

Misc:

  * Add installation, usage and test instructions to the Readme
  * Add travis powered CI
  * Elimenate Kernel#nil? calls
  * Add simple profiler
  * Simplify Sample helper definition
  * Add basic test suite