Implement Wasmtime's new API as designed by RFC 11. This is quite a large commit which has had lots of discussion externally, so for more information it's best to read the RFC thread and the PR thread.
* Add examples of linking and WASI
This commit adds two example programs, one for linking two modules
together and one for instantiating WASI. The linkage example
additionally uses WASI to get some meaningful output at this time.
cc #1272
* Add examples to the book as well
* More links!
* Ignore examples from rustdoc testsing
* More example updates
* More ignored