Async AC: Introduce irony-completion-stats-at-point

In order to detect interesting completion points a difference is made
between completion identifier beginning and completion context. It
should avoid unecessary requests for new completion list when the
context hasn't changed.
Async AC: Start working on the completion trigger mechanism.
Differentiates new completion context from new completion 'point',
will be used to request the irony-server process only when necessary.
Simple completion: Replace use of CXString by ClangString and null check.
Async AC: detailed completion only ATM is async.
Async AC: trigger manual `ac-update` + `ac-start` to generate completion.
Async AC: "Bundle" header completion.

It is not separated from the standard completion now. It will allow
further improvments such as doing the search on the C++ side in order
not to block the Emacs process.
Async AC: Add identifier-only completion.
Async AC: Fix broken (loop <...>) that caused an infinite loop.
Async AC: Add user triggered completion.
Async AC: Start cleaning up/tuning of CodeCompletion.cpp.
Mainly remove some unused code.
Async AC: Reduce size of completion request answers.
Make completion code a bit less messy/complex.
Async AC: Move the snippet support to a dedicated file.
Now the completion actions are "built in" irony-completion so it can
be reused by other completion backend eventually.
Remove legacy eproject.el.
Async AC: Correct usage (hopefully) of current parameter.
This fix an infinite loop that because typed text was expected to be
always present in a completion candidate.
Async AC: Candidate action fixed for header completion, add 'auto-retrigger'.
AC Clang: Sort completion results.
They are sorted in a semi-case-insensitive way. Strings that match
case-insensitively are then ordered depending on based
case-sensitivity:
- Foo
- Foo
- foo
- foo
- FooBar
- foobaR
- foobar
- foobar
- ...
Async AC: Basic support for 'classic' auto-complete.
Will be enhanced in order to add action that expand snippets.
Small documentation fix.
Async AC: Display [result-]type in the AC candidate.
Async AC: Expand snippet when possible with standard auto-complete.