Make changes for a Fedora RPM

This change adds an RPM file and makes some
minor modifications to the build in order to create
an RPM file which passed the Fedora review process.

For this spec file to work there has to be a tag named
`open62541-<version>`, e.g. `open62541-0.2`. However this
can be locally emulated by providing a sources file of the
same name, e.g. `open62541-0.2.tar.gz`.

An easier option is to use `tito` for a local build and
execute `tito --test --rpm` in order to build a local version
of the latest git commit automatically.

Also see: https://bugzilla.redhat.com/show_bug.cgi?id=1487578

.tito/packages/.readme

@@ -0,0 +1,3 @@
+the .tito/packages directory contains metadata files
+named after their packages. Each file has the latest tagged
+version and the project's relative directory.