Extended documentation for isapprox
Rewrote optional tolerances to named arguments
Removed isequaln, since it's pointless
Added missing hook to test floatapprox
Updated isapprox and isapproxn

* Improved API for providing tolerances using named arguments
* Simplified the generic constraints on all methods
* Dropped support for arrays - use map() or all() manually instead
Extended documentation for isapprox and isapproxn