[c-ffi] Add a new error-condition result type.

This helps writing better wrappers for C libraries where the
return value is used to signal if the function did error.
[doc] Add documentation about error-result.
[doc] Update release notes with latest changes to C-ffi.
Merge pull request #803 from fracek/c-ffi-error-condition

[c-ffi] Add a new error-condition result type.
Fixed copy-paste typo.
[c-ffi,dfmc,llvm] Added [s]size_t support as raw-c-[s]size-t
Merge pull request #761 from wvdschel/arm-linux-support

Added [s]size_t support as raw-c-[s]size
[c-ffi] Added a few unit tests for size_t/ssize_t.
Merge pull request #804 from wvdschel/master

[c-ffi] Added a few unit tests for size_t/ssize_t.
[dfmc-debug-back-end] Tabs to spaces.
[dfmc-typist] Fix comment typo.
[dfmc-modeling] Clean up whitespace.
[crt] Fix build of things using C-FFI.

Definitions for some primitives for the size_t / ssize_t work were
missing.
[common-dylan] Print function signatures rather than specializers.

This is useful when looking at errors / conditions when they're
displayed.
Merge pull request #805 from waywardmonkeys/improve-method-signature-printing

[common-dylan] Print function signatures rather than specializers.
[llvm] Add additional DWARF5 language constants.

This also updates to use the correct one for Dylan now that we've
been assigned one.
[dfmc,debug] Add operation-name for <method-apply>.
[OVERVIEW] Fix typo.
[llvm] Missing exports for new language constants.
[registry] Simplify c-ffi registry entries.

Fixes #749.