Improve examples further (#141)

* Rename examples so they appear in the right place

Some of them are moved into Config, others Linker, etc.

* Move examples out of doc_test

And reformat them in a godoc-friendly way.

* Rearrange comments

* Rename test for completeness

* Minor formatting so the wat code is copy-friendly

* More formatting

* Merge functions into example function

This is more godoc-friendly.

* Merge all the examples together

This reduces the amount of files while they are still broken down
into individual examples in the documentation.

* Move the remaining 2 examples

* Use log.Fatal* instead of panic

This follows what other packages are doing.

* Remove superfluous output

* Add externref example

* Fix some warnings found by golangci-lint

Author: fgsch