Build osmium_convert in order to be able to eventually replace osmosis

This provides a script to build the libosmium examples such as
osmium_convert (to convert from xml to pbf).

I initially tried a CMake ExternalProject setup, but this was more
complicated than I initially thought; this is the more elegant solution.

The goal is to eventually rip out osmosis, so that we no longer depend
on java for the cucumber tests.

References:

- https://github.com/Project-OSRM/osrm-backend/issues/1788

scripts/build_osmium_tools.sh

@@ -0,0 +1,15 @@
+#!/usr/bin/env bash
+
+# Builds command line tools shipped with libosmium for example osmium_convert
+# CMake build directory is build/osmium; binaries are located under build/osmium/examples
+
+
+# e: exit on first error, x: print commands
+set -ex
+
+BUILD_DIR=build/osmium
+
+cmake -E remove_directory $BUILD_DIR
+cmake -E make_directory $BUILD_DIR
+cmake -E chdir $BUILD_DIR cmake ../../third_party/libosmium -DCMAKE_BUILD_TYPE=Release -DBUILD_EXAMPLES=1 -DBUILD_TESTING=0
+cmake -E chdir $BUILD_DIR cmake --build .