cargo test --doc cannot find DLL on Windows

[termoshtt]

https://github.com/rust-math/fftw/runs/1044484751

running 3 tests
test src\array.rs - array::alignment_of (line 109) ... FAILED
test src\lib.rs -  (line 10) ... FAILED
test src\lib.rs -  (line 29) ... FAILED

failures:

---- src\array.rs - array::alignment_of (line 109) stdout ----
Test executable failed (exit code -1073741515).

---- src\lib.rs -  (line 10) stdout ----
Test executable failed (exit code -1073741515).

---- src\lib.rs -  (line 29) stdout ----
Test executable failed (exit code -1073741515).

[termoshtt]

exit code -1073741515

This means DLL not found. This happens only for doctests, it is similar to rust-ndarray/ndarray-linalg#229

[termoshtt]

CI is disabled in #104. This issue is kept opening until it will be re-enabled without failure

[termoshtt]

We should split tests for windows-msvc and windows-gnu environment. windows-gnu env seems to be broken.