Created new branch add-readme
Draft of introduction to sage-mode, including iandrus' suggestions and some installation guide.
Merged in jsrnielsen/sage-mode-jsrn/add-readme (pull request #1)

Easy introduction for setup and basic use of sage-mode
Renamed readme so bitbucket renders it
Documentation style fixes
Removed unused file
Fixed `sage-attach-this-file'
Updated installation instructions

Fixes #34
Added sage-view-default-commands
Fixes 33
Document sage-view-default-commands
Work around invalid LaTeX use for MathJax
issue #32