Add win32 travis build (#2)

* add mingw64 build to travis CI

* Make .travis-lin-mingw.sh executable

* .travis-lin-mingw.sh: make build dir

* show $PWD in travis-lin-mingw

* update .travis-lin-mingw.sh

* ---

* update .travis-lin-mingw.sh

* update p7zip cmd

* fix sign/unsign comparioson in usb.c

* revert call .travis.sh

* clean up .travis-lin-mingw.sh