Support time stamps other than integers starting from 1
Added the design documentation for Cox & Sandwich

Conflicts resolved by Feng, Xixuan (Aaron):
	doc/design/design.tex
	doc/literature.bib
	src/ports/postgres/modules/stats/cox_prop_hazards.sql_in
Documentation: Multiple changes to doc format

- Removed "Files" node from the left panel and allows to customize the
contents of the left panel by editing DoxygenLayout.xml.
- ARIMA: Reformated syntax to one arg per line and add results to
 example.
- Other modules:
    - Syntax arguments one per line, changed presentation of defaults
    - Revised menus, syntax, arguments, examples for consistency.
    - Corrected misspelling and other typos
Merge pull request #16 from madlib-internal/old_cox_design_doc

Added the Design documentation for Cox & Sandwich (Authored in summer, 2012)
ARIMA: Update online help to not use _diagnostics
Elastic Net: Remove buggy doc example
More clarification on coef_all and coef_nonzero