Yet more refactoring of manual

- Adds new section on naming variables and style convention
- Refactors linear algebra content out of Arrays
- Turn more lists of functions into tables
- Documents built-in Exceptions, symbol(), isnan, isinf, isfinite, info, warn
- Updates list of vectorized functions and documents @vectorize_?args macros
- Turns embedded HTML footnotes into ReST footnotes
- Fixes sectioning issue in Arrays
- More cross-referencing, especially for non-standard string literals
- Minor grammatical, language, spelling cleanup
- Remove user-specific output from sample Julia snippets