Installation instructions

[lkosmid]

@federeghe - I tried to build the software for the JOSS review and had a problem with the compiler versions. I tried several versions of gcc up to 4.9, and clang 3.8 but they fail to compile. It builds ok with gcc-5.4. So you can modify the requirements ("What you need" Section at README.md) as follows:
A modern compiler with C++14 support like GCC (version 5 or later) or LLVM (XX version or later) and the CMake building tool.

Also for configuring the project:
In case that you have multiple complilers installed in your system, you can specify a compatible compiler as follows:
CC=gcc-5 CXX=g++-5 cmake ..

[federeghe]

I added the requirement for GCC 5. It's strange that it does not work with clang 3.8 (it should according to their feature list). I will try in a few date and update accordingly the readme.

[federeghe]

I detected this error with clang 3.8:

src/statistical/test_ljung_box.cpp:209:90: fatal error: recursive template instantiation exceeded maximum depth of 512

That is not really meaningful for me, since there is no recursion in used templates. According to some website, it seems a bug of version 3.8 of clang compiler.

I confirm that clang 6.0.0 compiles successfully the software. I need some time to test versions 4.x and 5.x.

[federeghe]

Ok, clang 4.0 compiles the software. I changed accordingly the documentation.