make SafeLong constructor public
implement trig functions for Complex
give BigDecimal a faster sqrt method
Implement BigDecimal approximations of pi and e.

This is a work-in-progress. Currently we won't win any awards but at
least we'll be able to support the precisions that most people will
be intersted in.

We still need better precision for all the other methods in Trig but
at least this is a start.
Add spire.math.Searching to allow searching using Order[A].

This is an analogue to java.util.Arrays.binarySearch but implemented
using our specialized Order[A]. We also have a version for
IndexedSeq[A] to support things like Vector[A].

Consider adding implicits so that users can say arr.search(...).