Fix compilation when used as submodule

There were problems due to the use of GenerateExportHeader when using
this as git submodule. This has been fixed. Be sure to add
EXT_INCLUDE in parent project to include_directories.

Signed-off-by: Christian Rapp <0x2a@posteo.org>

Updated DocToc index

Signed-off-by: Christian Rapp <0x2a@posteo.org>

Incompatible API changes

First release