Simple test for MRPT approximate nearest neighbor search

Pipeline

1. Run ./install_eigen.sh: installs eigen linear algebra library; current version is Eigen 3.3.4.

2. Install a current version of MRPT: git clone https://github.com/teemupitkanen/mrpt.git, and specify the installation directory to the variable MRPT_PATH in cpp/Makefile (default is the directory that contains this repo).

3. make the test file in cpp folder and run it using cpp/test.