update function/after behavior to always call callback asynchronously.

also make sure callback is executed once for each call.
add test to ensure function/after keeps reference to call context
rename function/after to function/awaitDelay. see #140. see #139
simplify string/escapeRegExp
only create RegExp when needed on string/escapeRegExp
add number/isNaN. closes #136. closes #142

decided to not reuse number/isNaN on lang/is since there is no real gain.
Add array/sortBy
add number/ordinal & number/nth. closes #143
Add array/slice
Use array/slice instead of Array.prototype.slice
add `function/identity`. change `function/makeIterator_` behavior. closes #147

also add test to `array/sortBy` without a callback (make sure it uses identity
function).

this might break some code that expects the internal `makeIterator_` method to
return `null` or `undefined`... but since this is an internal method I don't
think it's a big deal (our code will work fine, all tests still passes).

one downside of the new `makeIterator_` behavior is that it will not throw
errors in cases where user forgot to pass the callback, which might make it
harder to spot why some code is giving the wrong output, but I think it is an
improvement overral since it will increase flexibility and this behavior might
be shared among multiple methods (identity is a good default behavior for
`array/map` as well).
update changelog
v0.8.0
add test for clearTimeout on function/awaitDelay and document it.
add un-padded 12-hour %l to strftime
change 12-hour format (%l) to include space prefix

this properly follows the typical implementation of this option
fix spec wording for strftime %l option
Merge pull request #150 from efleming969/master

add un-padded 12-hour %l to strftime
Accept leading zeros for &#39 in unescapeHtml

Fixes #151. Accepts any number of leading zeros for `&#39;`. This also
splits out the variuous escape sequences into a test for each one.
Clarify documentation for `{un,}escapeHtml`

Ref. #151 and #152.