Additional constructors/possible-classification for std::bitv

[Dretch]

I have written these functions for my own use, but I would like it better if they were inside std::bitv:

/**
 * Transform a byte-vector into a bitv. Each byte becomes 8 bits,
 * with the most significant bits of each byte coming first. Each
 * bit becomes true if equal to 1 or false if equal to 0.
 */
fn from_bytes(bytes: [u8]) -> bitv;

/**
 * Transform a [bool] into a bitv by converting each bool into a bit.
 */
fn from_bools(bools: [bool]) -> bitv;

/**
 * Create a bitv of the specified length where the value at each
 * index is f(index).
 */
fn from_fn(len: uint, f: fn(index: uint) -> bool) -> bitv;

(there are also corresponding to_bytes/to_bools methods).

As a separate but related issue, I think it would be nice if the bitv type was turned into a class and its internal data marked as private members.

As either of these requests pleasing to you? I can provide pull requests (with tests/docs/etc) if they are.

[catamorphism]

There's already a bug for the second issue: #2341 - I actually have a patch for this, but it's not working and I haven't gotten around to figuring out why.

Feel free to submit a pull request for the added functions! Thanks!

[catamorphism]

Closing this, but please do submit that pull request.