Bug fixes and unified library init/shutdown

Move allocator functions to their own file (#488)

* Move the allocator related functions to allocator.c

* Add overrides for the allocator functions

* PR Comments

Atomics support extended back to gcc 4.1.2 on Intel

Relaxed constraints on gcc+x86/x64 to gcc 4.1.2 (#482)

* Relaxed constraints on gcc+x86/x64 to gcc 4.1.2, added ARM and Itanium detection for gcc 4.4

Use CMake Threads module instead of manual pthreads linking

v0.4.3

Depend on pthreads via Threads rather than manually (#473)

Fix error info

Fixed issue where the wrong info was returned for some error codes.

Logging refactor

Add yaml file for aws_byte_buf_cat proof (#448)

* Proof harness for aws_byte_buf_cat with a fixed number of arguments

Task logging

Adds string tags to tasks and task logging for easier identification

Fix nasty overflow bug in high-res clock on 32-bit systems.

v0.3.15

Fixed typo that broke osx build. (#425)

Linux stack trace fixes

Parse (<function>+<addr>) backtrace format on POSIX systems (#422)

* Parse (<function>+<addr>) backgtrace format on POSIX systems #356

Compile warning fixes

Re-enabled unknown pragma warnings, wrapped CPROVER pragmas (#420)

* Re-enabled unknown pragma warnings, wrapped CPROVER pragmas

Miscellaneous cleanup

Fixes to clang-tidy failures in dependent libs (#418)

* fixes to clang-tidy failures in dependent libs

* fixed test harness asserts to prove to clang-tidy that compared values are non-null, initialized out params

* Fixed mis-used asserts and multi-eval of assert values

* preserve existing behavior