Download Windows headers from MinGW
Copy edit.dll to the app directory on Windows
Upgrade Just.Process
Copy the Windows headers next to metashell.exe and add it to the include path
Remove unused function
Disable tests that need a clang binary in CI
Fix SIGSEGV in pragma parsing with trailing whitespace

The pragma parsing algorithm caused Segmentation fault,
when the pragma handler tried to read the passed
token_iterators when only whitespace token(s) should've
appeared in the range. The reason is, that the algorithm
skipped over the whitespace token onto the EOI, EOF tokens.

Example test input:
"#msh environment add "
Merge branch 'pragma_parse_fix'