Migrate Rtio objects to true trait objects

This moves as many as I could over to ~Trait instead of ~Typedef. The only
remaining one is the IoFactoryObject which should be coming soon...
Remove rt::io::support

This removes the PathLike trait associated with this "support module". This is
yet another "container of bytes" trait, so I didn't want to duplicate what
already exists throughout libstd. In actuality, we're going to pass of C strings
to the libuv APIs, so instead the arguments are now bound with the 'ToCStr'
trait instead.

Additionally, a layer of complexity was removed by immediately converting these
type-generic parameters into CStrings to get handed off to libuv apis.
Remove IoFactoryObject for ~IoFactory

This involved changing a fair amount of code, rooted in how we access the local
IoFactory instance. I added a helper method to the rtio module to access the
optional local IoFactory. This is different than before in which it was assumed
that a local IoFactory was *always* present. Now, a separate io_error is raised
when an IoFactory is not present, yet I/O is requested.
Don't attempt to export uv functions directly
Migrate the last typedefs to ~Trait in rtio

There are no longer any remnants of typedefs, and everything is now built on
true trait objects.
Move as much I/O as possible off of native::io

When uv's TTY I/O is used for the stdio streams, the file descriptors are put
into a non-blocking mode. This means that other concurrent writes to the same
stream can fail with EAGAIN or EWOULDBLOCK. By all I/O to event-loop I/O, we
avoid this error.

There is one location which cannot move, which is the runtime's dumb_println
function. This was implemented to handle the EAGAIN and EWOULDBLOCK errors and
simply retry again and again.
Remove even more of std::io

Big fish fried here:

    extra::json
    most of the compiler
    extra::io_util removed
    extra::fileinput removed

Fish left to fry

    extra::ebml
Stop logging task failure to task loggers

The isn't an ideal patch, and the comment why is in the code. Basically uvio
uses task::unkillable which touches the kill flag for a task, and if the task is
failing due to mismangement of the kill flag, then there will be serious
problems when the task tries to print that it's failing.
Remove io::read_error

The general idea is to remove conditions completely from I/O, so in the meantime
remove the read_error condition to mean the same thing as the io_error condition.
Move stdin to using libuv's pipes instead of a tty

I was seeing a lot of weird behavior with stdin behaving as a tty, and it
doesn't really quite make sense, so instead this moves to using libuv's pipes
instead (which make more sense for stdin specifically).

This prevents piping input to rustc hanging forever.
Test fixes and merge conflicts
Remove std::io from ebml
Remove std::io once and for all!
Migrate std::run to libuv processes
Fixing some tests, adding some pipes

This adds constructors to pipe streams in the new runtime to take ownership of
file descriptors, and also fixes a few tests relating to the std::run changes
(new errors are raised on io_error and one test is xfail'd).
wrapping libuv signal for use in Rust
descriptive names
easier-to-use api
reorganize and document
Bring io::signal up to date with changes to rt::rtio
Another round of test fixes and merge conflicts