Fixes #454

We need to give the text view an opportunity to steal these keybindings
before they are taken by the plugin.

We can get a lot of motion events quickly, so we need to avoid doing any
extra work until the previous request finishes. Otherwise, we just spin
our wheels doing a whole lot of nothing.

Instead of waiting for the longest running completion provider to return,
update the available models immediately.

This fixes some annoyances with the snippet provider where we are
activating an unexpected item.

We need access to the source object after completion, so ensure that we
don't drop it.

I don't trust the use of gonce here, so just conservative and use gmutex.
Also, we can increase the ref of the sourcefile just to be safe.

We used to add checks everywhere for this, but it's easier if we just
give ourselves some protection against str*() functions dereferencing.

I was taking a look at this code and realized we should probably
standardize more of our components on using the fuzzy search so things
are consistent.

When we have an exact match, and enter is pressed, just insert a newline
rather than trying to go through the expansion dance.

We try to re-use results until the next reply comes in from clang (since
there is likely to be a high overlap). So this just does a refilter before
we submit the query.

These still turn out to be really useful at the top, so keep them in place
so things are more predictable.

This will reformat a block of function declarations. It tries to handle
a few conventions that we use in gtk apps. It does not handle everything,
nor can it handle generic input.

It also doesn't yet handle vtables.

This hasn't been accurate since we redid the layout grid and what not. So
just remove the type check.

This is useful when making interfaces and base classes

Clang can include <> in parameters, so we need to escape that for GMarkup.