Clean up .gitignore.

Which ones do you guys think we actually need to keep? I always do out of tree builds, so it turns out, I never need any of these.

Note, you can use a .gitconfig entry to specific a local ignore file for things that are consistent across your machine, like *.swp for vi or ~* for emacs.
Output from a direct make of the Makefile created by running qmake directly (which will build either directly IN the source tree or in build and release sub-directories if the "CONFIG = debug_and_release" option is used to build both variants at the same time).  Since I'm looking to add a suffix for debug builds so that the executables can coexist you may also see "src/mudlet_debug" and for Windows platforms both "src/mudlet.exe" and "src/mudletd.exe" (but they'd both already be taken out by line 17  for "*.exe".