Use Lambdas and UFCS in std.algorithm examples.

Better represent Lambda syntax and UFCS in the map/filter/reduce examples in std.algorithm.
Fixes Issue 5359 - isDelegate should work for types and expressions.
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.
fix Issue 3789 - Structs members that require non-bitwise comparison not correctly compared
Merge pull request #1193 from 9rnsr/fix3789

Issue 3789 - Structs members that require non-bitwise comparison not correctly compared
Merge pull request #1190 from chadjoan/patch-4

Use Lambdas and UFCS in std.algorithm examples.
Merge pull request #1192 from AndrejMitrovic/Fix5359

Issue 5359 - isDelegate should work for types and expressions.