Add some information about modelsql special functions, readme,
fix russian char and fix image fix

Closes #38
Fix minor issues
Ensure that all links to trytond doc refer to 3.2 version
library_demo_module added, changed field functions to apply on library example
Merge branch 'master' of github.com:hiaselhans/tryton-documentation

Conflicts:
	developer_guide/basic_concepts.rst