Remove .gitignore file

Don't ignore things like temporary editor files. This is something that
the system or user exclude file should ignore.

Signed-off-by: Marcus Karlsson <mk@acc.umu.se>
Ignore generated files

Files that are actually generated as part of the build system should be
ignored at the project level. Add them to the ignore file.

Signed-off-by: Marcus Karlsson <mk@acc.umu.se>