Project refactoring, resolves #17

Related issue #17.

New structure:

hpg-libs
 |
 |  C
 |   | build: libhpg.a
 |   | SConscruct
 |   | src: commons, aligner, math, bioformats, containers
 |   | test
 |  C++
 |   | build: libhpg++.a
 |   | SConscruct
 |   | src: commons, bioformats, ...
 |   | test
 |  third-party
 |   | htslibs
 |   | samtools
 |   | argtable
 |   | ...
 | README.md
 | LICENSE
 | ...