Initial hackish implementation of inlining

[davidmalcolm]

I had a go at implementing function call inlining ("inline substitution")

This is nowhere near ready yet (see the various TODO and FIXME notes), but hopefully is interesting.

[vstinner]

Oh great! FYI my motivation to write FAT Python was your patch https://bugs.python.org/issue10399 (funtion inlining)! IMHO we will get visible speedup on macrobenchmarks when the function inlining will be fully functional.

[vstinner]

I made changes to your code:

• fix Config constructor: initialize inlining attribute (and document it with a comment)
• respect the configuration and fix the unit test on config
• document the optimization and its configuration in doc/ (optim, config, changelog)