Test suite

[leotrs]

Implement tests by comparing sphinx's output to hard-coded HTML.

• Statement contianing math
• In sub-step: Statement contianing math
• Statmeent made up of a single latex symbol
• In sub-step: Statement longer than one line
• Statement longer than one line
• Test that :step:lbl and :step: some_latex are parsed correctly
• Test display math in regular text, theorem statements and steps and sub-steps.
• Reference equations using :eq:
• author directive
• abstract directive
• contents directive
• test for :prev: and :prevn: tags