Migrated isapprox() to base
Added test suite for isapprox()
Documentation for isapprox()
Removed duplicate definitions of rtoldefault and atoldefault methods
Test and export hooks for isapprox
Simplified implementation for real nonfloats as well as for complex numbers
Updated documentation for isapprox()
Merge pull request #3408 from tlycken/isapprox

Isapprox -> base
use complex(x) instead of complex(x,0) in isapprox
implemented detach() and attach() in multi.jl