Conditionally compile the `sorted` assertion

This closes #14. Tests now pass. Version was also bumped to 0.2.1

Add `key` documentation and bump version.

Project is now at version 0.2.0.

Add test and document a `sorted` method.

This method allows for assertions of whether a forward range is sorted
through the `std.algorithm.isSorted` function. It also bumps version to
0.1.0.

Add basic implementation of "comparison" helpers.

This closes #10. Tests now pass. It also bumps version to 0.0.11. We
should start developing ways to clean-up the codebase and tests.

Replace `assertThrown` and `assertNotThrown`.

This reimplements this logic in a really simple manner. Though it may be
a little less memory efficient than the `std.exception` functions, this
is a nicer implementation for us. It also bumps version to 0.0.10.

Fix and add tests for a `should.Throw` bug.

This fixes a bug which disregarded negation on `should.Throw`. In other
words `should.not.Throw` didn't work as expected. It also bumps version
to 0.0.9.

Add initial `should.include` implementation.

This closes #12, fixes the tests and bumps version to 0.0.8.

Add basic implementation of `length` assertions.

This closes #5. Tests now pass. More tests should be added, but I think
this is a reasonable implementation. There's nothing to do here, really.
Probably deciding which types to compile for and doing type conversions
is the real trouble with all functions in this library.

This also bumps version to 0.0.7.

Add basic implementation of regex matching.

This currently only works for string types. On a better implementation
it'd support making regex match assertions about any type convertible to
strings, but it's a trivial problem to solve at the client's side.

This, therefore, closes #1 for now and bumps version to 0.0.6.

Fix `.exist` instantiation for struct types.

This should close issue #6 and it bumps version to 0.0.5. I'm waiting
for @pataroose'ś feedback before closing it.
We should add better tests for struct and class instances usage.