Minor changes to Rust Language FAQ

- Change long inline code to code block
- Replace double-hyphens with en dash
- Miscellaneous rephrasings for clarity

**Edit**: Trivial `commit --amend` to change the commit message slightly.
Looks like this line [caused a test to fail](http://buildbot.rust-lang.org/builders/auto-mac-64-nopt-t/builds/2713/steps/test/logs/stdio).  Maybe the culprit is the removed backticks?