Turning on warnings about documentation comments.

Given that the project builds with -Werror, the documentation comment
warning has been forced to stay a warning via -Wno-error-documentation.
When the project is free of documentation warnings, this should be
removed.

Warnings about documentation comments containing @deprecated but the
actual declaration not having a deprecated attribute have been disabled
via -Wno-documentation-deprecated-sync. Turning this on and fixing the
warnings will result in a cascade of new warnings relating to using
deprecated APIs.

Issue: PLCR-543
Fixing the bulk of the documentation warnings.

This leaves a handful of warnings about using '@sa @ref async_safety'.
Clang thinks that the '@sa' command has an empty paragraph in this
case, but it appears to be a false positive and a bug in Clang.

Issue: PLCR-543
Working around Clang’s dislike of @sa @ref.

This is the last of the documentation warning fixes, so the
-Wno-error=documentation flag is being removed and documentation
warnings will be errors from here out.

Issue: PLCR-543
Removing the deprecated plcrash_async_read_addr function.

Issue: PLCR-543
Add deprecated attributes to deprecated members.

This fixes warnings about the doxygen comments not being in sync with
the attributes on the members. This should be the last of the
documentation comment warnings and -Wno-documentation-deprecated-sync
has been removed.

PLCR-543
Fixing return types.

When plcrash_async_read_addr() was removed in commit 1eb3c7b, the call
sites were not updated properly. plcrash_async_task_memcpy() returns
plcrash_error_t and not kern_return_t.

Issue: PLCR-543
Removing leading whitespace.

Issue: PLCR-543
Documenting the special handling of v1 reports.

Issue: PLCR-543
Narrowing the scope of diagnostic ignore pragmas.

Issue: PLCR-543
Ensure that a code type is always set.

This is currently impossible to reach, but if more processor info encodings are added this code will have something to fall back onto.

Issue: PLCR-543
Fixing documentation comment tags.

These were found by -Wdocumentation-unknown-command, which Clang
disables by default because it’s too noisy. In the case of the
PLCrashReporter code, it continually warns that 'internal' is not a
known command.

Issue: PLCR-543
Adding the concept of external deprecations.

An externally deprecated definition is marked deprecated for external
clients only. This allows the framework implementation to use the
definition without receiving deprecation warnings/errors.

Issue: PLCR-543
Stop using the deprecated sharedReporter in tests.

Issue: PLCR-543
Add a sanity check for the processInfo property.

Issue: PLCR-543
More autorelease, less memory leaks.

Issue: PLCR-543
Merge branch 'bugfix/PLCR-543-fix-documentation-warnings'