Mention that Numba no longer has distinct `@jit`/`@autojit`
Add table comparing installation and porting effort for runtimes.

There are still a few issues with the table:

- I cannot make the width of any column larger than what is needed to
  fit the first column.

- reST table options `:header-rows:` and `:stub-columns:` produce
  incorrect LaTeX code (blank line in the argument to `\textbf{}`)
Credit EuroSciPy2013 reviewers.