NumberHelper patch

As mentioned in this discussion I've started consolidating and refactoring the helpers.

The attached patch introduces a new API for some methods in NumberHelper. The goal is to consistently use an options hash instead of ordered parameters.

Affected methods

1. number_with_delimiter
2. number_with_precision
3. number_to_human_size

These three methods can now, like the other NumberHelper methods, take their arguments as an options hash. Examples:

number_with_delimiter(98765432.98, :delimiter => " ", :separator => ",") 
number_with_precision(389.32314, :precision => 0)
number_to_human_size(1234567, :precision => 2)

Reasons

IMO it has become kind of a Rails best practice to put additional behavior for a helper method in an options hash. This makes it easier for programmers because one doesn't need to remember the order of parameters - we can just pass it in in every order that we like.

NumberHelper has been inconsistent with this: number_to_phone, number_to_currency and number_to_percentage all take hashes whereas the three methods mentioned above have named and ordered parameters. In order to provide a consistent API (at least within a given module) I think that all methods should have a single interface (number as the first parameter and an options hash with sensible defaults as the second).

Documentation

I've added documentation for all changes that affect the public API. This basically means I've switched existing documentation to suggest the new API and added notes that the old API is still supported.

Tests

All existing tests pass. I've added tests for all methods to test the functionality of the new API.

Implementation notes

Some of the code is really redundant because I want to support two different APIs at the same time. If the old API gets dropped, things start to be a lot cleaner. If you want, I can also post another patch that only supports the new API.