add rustdoc comments with examples for the string versions of to_base64 and from_base64
Add comments for the implementations of from_base64 and to_base64 for .
move rustdoc comments so that they attach to the functions rather than the impl blocks.
Doc review, as requested :-).

Mostly just phrasing things differently, which is a matter of taste. Feel free to use or not use any of the changes I'm suggesting.

I would say this one thing should be changed, though, not necessarily the way I changed it here.

     * Convert any string (literal, `@`, `&`, `~`)
     * that contains a base64 encoded value, to the byte values it encodes.

If this structure is going to be used, either the entire clause, 'that contains a base64 encoded value', should be bracketed by commas, or the comma at the end of the clause should be removed.
Merge pull request #1 from danluu/silly_style_changes

Doc review, as requested :-).
update copyright notice on base64.rs
Change to 4-space indents in code examples
auto merge of #5879 : astrieanna/rust/document_std_base64, r=catamorphism

This adds examples for the methods in std::base64.

Each example is complete in the sense that you can copy-paste it into a file and compile it successfully without adding anything (imports, etc). The hardest part of figuring out how to use this was figuring out the right import statements to put at the top.