Bump version to v0.2.6-dev.
Removed conda (relocated to github.com/tpn/enversion-dist/conda).
Update README.md with installation instructions.
Tweak/fix README markdown.
Set version to 0.2.6.
Bump version to v0.2.7-dev.
Add section on upgrading and custom environments.
Add TL;DR Installation/Quick Start section.
Add links and tweak heading names.
Merge branch 'master' into issue11-limit-file-size