add mfr_installer to get plugin requirements
document mfr_install
exclude plugins if they are not compatible with the python version
code pygments fails in py3
command to install is mfr install instead of mfr_install
use plugins rather than modules or packages
mfr install must take an argument [plugins]
Merge branch 'feature/plugin_exclude' into feature/installer
exclude packages' test directories
capitalize CLI
mfr install requires a plugin list or all
print message if given path doesn't exist
use plugin rather than plugins
fix constants
dont pin dependencies
move arg validations outside of helper
handle bad commands and misc code review changes
Merge pull request #110 from asmacdo/feature/installer

Feature/installer
Merge branch 'dev' of https://github.com/CenterForOpenScience/modular-file-renderer into feature/mfr_pdf
fix use of get_assets_from_list