Fixes issue where dependent crates can fail to build while linking on…

… some systems ([#3]).

Mainly fixes, but also some shrinkage of the public api. v0.4.0

- Upgrade to `autotools` 0.2, updating the usages to be compatible with the
  new public api.
- (Hopefully) Fixes issue where the autotools build can intermittently fail
  ([#1]).

Pin to autotools 0.1 since 0.2 appears to break jq-sys.

Small release, deprecating a duplicated method, adding docs.

No more direct building - let the caller do it.

Ditches build.rs in favor of providing an API for the sys crate to do it
instead.

This is aimed towards spliting the building and the linking such that
the -sys crate is always the one doing the linking, regardless of
whether or not the -src crate is being used.

Initial release.