Add optional unicode operators.

I'm not sure if these will catch on, but it's nice to be able to
support the canonical mathematical symbols.
equality operators
fix error
Remove unused imports.

This commit removes a whole bunch of unused imports. It also adds the
-Ywarn-unused-import option under 2.11.
Remove spire.implicits._ imports from main code.

This will hopefully help things compile faster (or avoid
recompilations) but also makes it easier to be clear about
which code depends on which code.

The wildcard imports from spire.implicits._ and spire.math._
are really useful when authoring code, but are usually
much broader than actually needed.
Reduce spire.math._ imports.

Since spire.math is such a big package, this change makes
it easier to be clear on what is actually being used.
Especially with methods like max (which are provided by
scala.math, spire.math, and also many types) it can be
confusing to use a wildcard import.

Hopefully this will also make recompilation a bit easier.
Reduce spire.algebra._ imports.

Like the preceeding commits, this is designed to try to
limit visibility a bit. It's probably less essential
than the other two commits, since spire.algebra doesn't
contain any implicit conversions or important methods.

I've left wildcard imports in places where a file needs
more than 6-7 types from the package.
Update doc for Util
Raise the treshold in GeneratorTest from 0.3% to 0.35%
Add Well19937a and Well19937c PRNGs
Fix doc for Well19937a and Well19937c
Fix formatting (remove spaces)
Fix performance issues in Well512a, Well1024a, Well19937a, Well19937c

Keeps the previous implementations in comments as they serve well for documenting the relationship between the variable names in the original algorithm and their expanded index mappings.
Add Well512a, Well1024a, Well19937a, Well19937c to RandomBenchmark
Add Well44497a, Well44497b; Update GeneratorTest and RandomBenchmark
Fix typo in RandomBenchmark
Remove tempering constants from Well44497a
Fix modulo premature optimization bug in Well19937a, Well19937c, Well44497a, Well44497b and raise the treshold in GeneratorTest from 0.35% to 0.38% to make 19937a/c pass.
Replace costly modulo operation with 2 ifs and addition/substraction
Remove old implementation (Well512)