Type state analysis

[Richard Andrew Cattermole (Rikki)]

This proposal introduces a new semantic pass, that uses an IR to 
analyse memory transfers and the different states it can be in.

It is the bleading edge on program security, that would enable 
other memory analysis solutions such as isolated (immutable 
references ala Midori).

It enables:

- To prevent reads to uninitialized variables
- Prevent reads, writes, method calls to null objects
- Logic errors such as trying to read from an unopened file
- Is a framework to analyse unreachable vs reachable variables

It does not affect the type system.
Additional information must be provided by the user if they want 
to go beyond the defaults.
The default type state of each variable is meant to be as close 
to provable by the compiler, with user assistance like null 
checks.

A key premise is that newer edition ``@safe`` function will not 
be able to call the older ``@safe`` function.
This drastically simplifies decisions.

The end goal of this is to enable D to become temporally safe, 
which is critical to D's future (see the recent US government 
report on memory safety with specific mention towards temporal 
safety).
Without this, the framework required to do temporal analysis does 
not exist, and what would otherwise be very clear decisions 
become arguable at best, at worst complete unknowns.

For each variable declaration I am proposing a default type 
state, along with manual specification of the input and output 
states it may be in by using the UAX31 Medial character 
``identifier'input'output``.

This proposal was born out of necessaity after failure to solve 
issues surrounding isolated, and it too required a similar IR to 
be built.

I recognize that this could be a bit costly, but due to the 
potential performance wins as well as memory and logic safety, 
this is an absolute must if we want to be competitive.

Latest: 
https://gist.github.com/rikkimax/eed86a7061445a93f214e41fb6445e40
Current: 
https://gist.github.com/rikkimax/eed86a7061445a93f214e41fb6445e40/a8fffb5725904c6f5d74052d9c974a8f5d453fb0