Transfer repository information from SourceForge to GitHub

[murrayrm]

The TX-TL modeling toolbox has been shifted from SourceForge to GitHub, with commit history preserved. The issues on SourceForge have been shifted to GitHub as well, using a python script that transfers over the information: https://github.com/ttencate/sf2github

There are a few remaining items that need to be done:

• Transfer information from SourceForge wiki to GitHub wiki
• Update the list of users to match GitHub IDs: https://github.com/BuildACell/txtlsim/import/authors
• Put a notice on SourceForge indicating that this repository has shifted to GitHub

[murrayrm]

Information from SourceForge wiki has been transferred to GitHub. Information from SourceForge discussions has been transferred to GitHub. A notice has been posted on SourceForge indicating the shift to GitHub.

Remaining item is to update user IDs. For this we need Zoltan to create a GitHub account.