Add missing exclamation marks to names of mutating linear algebra functions

[johnmyleswhite]

The "backend" layer of the linear algebra system currently violates our design decision to require that all mutating functions include a ! in their names. For example, A_mul_B(C, A, B) should really be named A_mul_B!(C, A, B) because it mutates C.

[ViralBShah]

Reasonable. +1.

[lindahua]

Sounds good to me.

This may probably break quite a few of my packages. However, the fix would be easy.

[ViralBShah]

We should be able to avoid breakage with deprecation.

[ViralBShah]

We should definitely try to do this for 0.2. Will probably require parser changes, but is relatively easy. Cc: @JeffBezanson

[Keno]

Bump.

[JeffBezanson]

Parser changes not needed, since the parser doesn't generate calls to mutating versions of these functions.

[ViralBShah]

How about doing this with the 3-arg forms of solve as well?