Use Lambdas and UFCS in std.algorithm examples.

Better represent Lambda syntax and UFCS in the map/filter/reduce examples in std.algorithm.
Use approxEqual for doubles in some examples.

Replaced a few instances of doubles being compared with == in std.algorithm's examples.  They are now compared with approxEqual.  This should encourage better practices, since floating point numbers can experience rounding errors that would make direct equality checks fail in situations where they are expected to work.
Merge pull request #1190 from chadjoan/patch-4

Use Lambdas and UFCS in std.algorithm examples.