Expands the API and reroutes all allocation through GlobalCtx

[icmccorm]

This is the second part of the change mentioned in #4. It's dependent on #9

New Types

• Adds Span as a wrapper for usize
• Adds AllocId as wrapper for usize
• Adds BorTag as a wrapper for usize
• Adds AllocInfo, a metadata object for each allocation. Contains the ID, base, bounds, size, alignment, and Tree for an allocation. The tree is currently a pointer to c_void, as we haven't yet added the state of the borrow tracker.
• Adds Provenance, which contains an AllocID, a BorTag, and a pointer to AllocInfo.
• Renames GlobalState to GlobalCtx
• Renames BsanAllocator to BsanHooks
• Factors out BsanAllocHook from BsanHooks to use for an Allocator implementation that's also Copy

Expanded Global State

• Adds hooks for printing (Print) and terminating (Exit).
• Adds custom print! and println! macros that use GlobalCtx
• Adds ui_test! macro, which will print only if the ui_test feature is enabled.
• Adds Hello, world! UI test which verifies that we've initialized our runtime.
• Adds BVec, BHashMap, and BVecDeque wrappers that enforce use of the GlobalCtx as an allocator.

Additional API Functions

• Switches to using return pointers for Provenance values
• Adds bsan_deinit endpoint that deinitializes the state of the runtime. Called automatically on termination.
• Adds endpoints for setting and clearing provenance from the shadow heap. (bsan_shadow_copy, bsan_shadow_clear)
• Adds endpoints for popping and pushing stack frames (bsan_push_frame, bsan_pop_frame)
• Adds endpoints for allocation (bsan_alloc, bsan_dealloc, and bsan_alloc_stack)
• Adds endpoints for storing and loading provenance values from the shadow heap (bsan_store_prov, bsan_load_prov)

[icmccorm]

ARM linux is disabled in CI due to #6