Proto commits in ad-freiburg/loom

These 3 commits are when the Protocol Buffers files have changed:

Commit:a7df52a
Author:Patrick Brosi
Committer:GitHub

Native protocol buffers support for MVT generation (#42) So far, transitmap used libprotobuf for the MVT tile generation (MVT uses protocol buffers as a container format). This dependency created more and more problems, as the minimum C++ standard requirement went up to C++-17, it suddenly added abseil as a dependency, and the standard CMake find script for Protobuf did not yet handle the abseil dependency correctly. This PR replaces libprotobuf completely by native MVT protocol buffers writing. This was not hard to do (it added around 200 LOC), as the MVT protocol buffers format is straightforward.

This commit does not contain any .proto files.

Commit:19ccc27
Author:Patrick Brosi

update cppgtfs and util, adjust existing code to lib updates at a few places

The documentation is generated from this commit.

Commit:14dd011
Author:Patrick Brosi

add MVT vector tiles output mode