Add Windows to the CI

[etra0]

I added Windows to the CI. I had to force the usage of NMake to make sure it could run in more places without requiring a specific version of Visual Studio.

The Windows CI fails because it fails at some tests, but the CI itself is correct. It seems that the tests that are failing are because of the handling of new lines in Windows, which should be fixed in another PR.

[etra0]

Specifically, I got this failure:

Spec failure

``` Failures: 1) Lexbor::Node to_pretty_html work Failure/Error: node.to_pretty_html.should eq t Expected: "

\r\n Haha\r\n \r\n 11\r\n \r\n

" got: "

\n Haha\n \n 11\n \n

" # \spec\node_spec.cr:423 2) Lexbor::Node to_pretty_html work, not serialize next node Failure/Error: node.to_pretty_html.should eq t Expected: "

\r\n Haha\r\n \r\n 11\r\n \r\n

" got: "

\n Haha\n \n 11\n \n

" # \spec\node_spec.cr:437 3) Lexbor::Node to_pretty_html work Failure/Error: node.to_pretty_html.should eq t Expected: "\r\n \r\n \r\n

\r\n Haha\r\n bla\r\n \r\n 11\r\n

---

\r\n 12\r\n \r\n \r\n \r\n

\r\n" got: "\n \n \n

\n Haha\n bla\n \n 11\n

---

\n 12\n \n \n \n

\n" # \spec\node_spec.cr:464 4) Lexbor::Node to_pretty_html work Failure/Error: parser.to_pretty_html.should eq t Expected: "\r\n \r\n \r\n \r\n \r\n j\r\n \r\n \r\n" got: "\n \n \n \n \n j\n \n \n" # \spec\node_spec.cr:488 Finished in 445.73 milliseconds 392 examples, 4 failures, 0 errors, 5 pending ```

[kostya]

wow thanks.