Fix benchmark project after syntax refactor
Fix incorrect package declaration in Ops.
Add benchmark to main project aggregate.
Make some traits private that needn't be public.
Make more traits private where possible.
More minor refactorings/clean-up.

Move Literals out to spire.syntax. Make some more objects/traits
private[math] where possible.
More code docs and doc-related code clean-up.
Numeric doesn't extend Field anymore.

Aside from some other minor fixes/refactors, this also makes Numeric
only extend Rig now, rather than Field. Note that / still exists with
Numeric, but it comes from inheriting just MultiplicativeGroup, rather
than Field.
Make Numeric[A] extend Ring[A] instead of Rig[A].

This change enables some useful implicits involving literals. Arguably
those implicits should not depend on Ring[A] but for now this is the
simplest way forward.
Improve ops macro dependency situation.

This change allows Spire's 'core' project to take advantage of the Ops
macros. This means that we can actually use readable, symbolic
operators in files like Complex.scala without paying a performance
penalty for doing so.

Finally, we can have our cake and eat it too!
Update README.md
Fix typo in README
Merge remote-tracking branch 'jedesah/patch-2' into 2.10.0
Touch up MetricSpace and implement laws.
set up travis hooks
Fix complex refactoring bug
Merge remote-tracking branch 'tixxit/topic/metricspace-laws' into 2.10.0
updated .travis.yml build
Add travis build status to README.md
Use rational version of GCD for GCD.