Add requirements.txt to python script
Merge pull request #36 from kovrus/python-script-installation

Add requirements.txt to python script, facilitating easy installation of python pre-requirements using pip.
Add Ruslan Kovalov to the AUTHORS/CONTRIBUTORS files.
Add a .md extension to go/README.
Update the content of go/README.md to Markdown.
Convert go/README to Markdown format.
Remove the nearly useless go/ENV file.
Reformat merkle_tree_go.cc.