Fix API docs

[mstechly]

There are several minor issues with how API docs are being displayed:

• Base classes should have full path (e.g. BaseModel)
• Would be nice to add links to the source code.
• For all the properties remove "returns" and just state what the property is.
• Add explanation for AnnotatedValue at the top of API docs (and perhaps some other objects which are not explained
• Make enums list their values
• Update docstrings to make them more descriptive and helpful, as some are very short (e.g. for Routine
• Make any mathematical expressions display with Latex
• Change styling for class methods (such as find_descendants) as right now the header with the class name looks same as Parameters and it's hard to see what's the structure
• See if any Raises fields are missing from the docstrings
• compile_routine –> typing is not displaying properly, it should load the types from the overload.
• AddPassthroughPlaceholder: move the docstring from __init__ to class.
• While working on Add concepts pages #38 I thought that it would be nice to add links to reference on concepts/precompilation docs page, though I wasn't sure what the syntax is, so decided not to do that right away.