Implement stacktrace from current exception for MSVC

[huangqinjin]

Original stacktrace from std::exception_ptr is not possible currently. std::current_exception() makes a copy of current exception object into returned std::exception_ptr. So the tracking of the original exception object and its stacktrace are lost.

Support for nested exceptions is not much meaningful IMO, it complicates the implementation (see the last commit). Without nested exceptions support, one can always get stacktrace from current exception immediately after entering catch block, but it loses the original stacktrace for rethrow_after_other_exception case.

The exception object is destroyed by __DestructExceptionObject exported from vcruntime.dll, there is no simple way to cleanup stored traces in time unless override __DestructExceptionObject.

[apolukhin]

Very impressive!

Added some comments and nitpicks

[coveralls]

coverage: 86.308%. remained the same
when pulling f76e128 on huangqinjin:msvc-stacktrace-from-current-exception
into 351b03d on boostorg:develop.

[apolukhin]

Many thanks for the great PR!

[ingo-loehken]

it is possible to track nested exceptions and to map exception_ptr to their callsite, but it can (imho) only be done via IAT Hooking functions in each affected library. Alternatively one may also apply EAT Hooking, if it is guaranteed that the shared libs are not loaded dynamically into foreign processes ... i.e plugin libs into excel or inproc ole/com or other stuff.

Besides that, the perf and abilities of boost::stacktrace are quite impressive. The dep to COM Init should be removed for Windows, if resolving symbols. The implementation of seems to bypass the CoInit and therefore avoid apartment model collisions.