Thanks to Sebastinas

With this commit it is possible to pass the path to an configuration
directory. Thanks to Sebastinas

Other changes:
  * Updated Makefile
  * Update Manpage

Thanks to Sebastinas

Thanks to Sebastinas

Thanks to n0nsense

With this commit it is possible to activate a smoother scrolling
by setting smooth_scrolling in the zathurarc file to e.g. 2.0.

This patch appends slashes to directories in cc_open. In addition
lines in zathurarc that do not end with a new line won't be
ignored anymore.

Thanks to Trundle

This commit does not allow every shortcut
when the buffer is not empty

Thanks to vimprobable

This commit makes it possible to define and use special keys
like <Space> on their own or in combination with a modifier:
<C-<Space>>.

In addition the evaluation of the keypress has been changed, so
that the order of the bindings do not matter any longer.