* chore: make example in README solver agnostic
And add a note on how to use a specific solver
* docs: add comments to README code
* Update requirements.txt
* docs: update README to reflect swiglpk as a dep.
swiglpk is a hard dependency now, so that 'pip install optlang' works out of the box.
* docs: update install instructions
Swiglpk is now a hard dependency so the installation instructions are updated accordingly.
* docs: update dependency versions in readme
* docs: update contributing guidelines
And add CONTRIBUTIONS.md file
* docs: update readme, paper and documentation
Add target audience to paper and docs/index
Add solver problem capabilities to readme
Move installation issue from readme to docs/installation
* test: remove libglp from travis.yml
* docs: highlight 'modeling language'
* docs: change paper title
* Some minor writing fixes (#57)
I made some minor writing fixes, to be adopted before acceptance in JOSS (https://github.com/openjournals/joss-reviews/issues/139)
