Installation fails on MacOS X

[ajaust]

When installing preCICE from source on MacOS X, installation of the Python bindings fails. Installation was conducted using pip.

I observed two different problems:

1. The preCICE headers could not be found. This could normally be solved by setting CPATH to preCICE's include/ directory.
2. clang failed to link the bindings against preCICE as it does not find lprecice. I was not able to fix it. Even setting DYLD_LIBRARY_PATH to the lib/ directory of preCICE did not fix this issue.

I started to reproduce the issue in a workflow, see #138, for a system installation into /usr.

[ajaust]

Just as an addition: It seems that the compilation and installation could be fixed easily by using pkg-config (see #135). It is still unclear how to make the installed preCICE library findable/known to MacOS X such that it is available when import precice is called.