include tutorials in doc, rework text

- tutorials are now included in Example doc section
- for this: "if main" needed, fix finding burnman if not installed
- Example section is somewhat work in progress
- experiment with including code directly
- include a picture as a test
doc: move examples to beginning
play with latex format
include cig title in pdf
doc: add overview, fix examples
Merge pull request #35 from tjhei/doc_updates

[WIP] Doc updates