Exclude all build* files/directories @ root level

I tend to create multiple build paths at the root of the
project, for testing various configurations. So I'll have
all of `build/`, `build-somebranch`, `build-otherbranch`,
etc. sitting around.

This PR updates the `.gitignore` for the repo to exclude
`/build*`, meaning _anything_ with a name that starts with
`build`, if it's located at the root of the repository tree.

Author: ferdnyc

.gitignore

@@ -1,5 +1,4 @@
-build/
-build/*
+/build*
 *.DS_Store
 .pydevproject
 .settings