docs/guide/interfaces/api: small fix
docs/quickstart: missed Fedora mention
docs: fix several typos
docs: better workding
docs/api: replace budgets in examples with sheets
docs/api: update example recommended usage

Remove usage of budgets, added sheets/items to the example since it is a
good starting point (from my understanding so far).
docs: fix some build warnings
demo/index.rst: update to new development server instance
Merge pull request #224 from alon/feature/more-docs-fixes

Feature/more docs fixes
Merge remote-tracking branch 'upstream/develop' into develop