Fix crashes on Windows by replacing ScopedLpwstr with std::wstring.

[soerlemans]

After further investigation into #42.
It seems that the crashes have to do with usage of std::unique_ptr itself.
Even using the correct using ScopedLpwstr = std::unique_ptr<WCHAR[], LpwstrDeleter>;.
With accompanying delete[] does not fix the issue, and the issues persist.

So in order to fix the issue instead of using std::unique_ptr<> we use std::string and std::wstring.
As they abstract direct usage of new[] or delete[].
And the issue with std::unique_ptr<> seems to occur from some kind of mismatch between the C++ runtime allocator and the allocator Windows uses.

Other people who use MultiByteToWideChar() generally use std::wstring:
https://stackoverflow.com/questions/14184709/is-this-code-safe-using-wstring-with-multibytetowidechar

I think in order to fix this issue it is better to follow suite since it seems like the most straightforward way to go.

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 77.60%. Comparing base (1865e69) to head (1d35426).

Additional details and impacted files

@@           Coverage Diff           @@
##           master      #43   +/-   ##
=======================================
  Coverage   77.60%   77.60%           
=======================================
  Files           4        4           
  Lines         250      250           
  Branches       76       76           
=======================================
  Hits          194      194           
  Misses         33       33           
  Partials       23       23           

Flag	Coverage Δ
unittests	77.60% <ø> (ø)

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[hrantzsch]

Thank you for working on this. Do you think you could come up with a test case that reproduces the crash? So far I have not been able to.

While avoiding the ScopedLpwstr construct and just using std::(w)string is certainly desirable, I'm hesitant to make those changes without a clearly reproducible issue.

[soerlemans]

So I just did some more testing and apparently I accidentally linked to MSVCRTD.lib.
Whilst trying to fix some stuff.
I got a warning in conflicts that I oversaw and that ended up being the underlying issue behind the bug.
Since I working on including this library in a project which uses an SDK, and it conflicted with that.

As for the PR I would still like to see the changes merged.
Or atleast the std::unique_ptr<WCHAR> type changed to std::unique_ptr<WCHAR[]> (as this specialization will automatically use delete[]).
Removing the need for an explicit deleter.

Is there anything I can/should do in order to get the PR merged?