Fixed #36.

* bootstrap: Newly added.
* template/x86_64-unknown-linux-gnu/site-config.jam: Added `asan2line`
  launcher.
* template/x86_64-unknown-linux-gnu/user-config.jam: Factored out setting of
  the paths to DocBook XSL and DTD. The setting will be modified by
  `bootstrap` script during deployment.