We use $1 instead of $(1) or $p instead of $(p) when possible,
except when building variable names (pkg_$(p)_name for example,
but also $(dep_fetch_$(1))).

This method dates back from the beginnings of Erlang.mk
and should not have been used for around a decade by now.
Adding "git" to the offending dep lines is enough to upgrade.

Use the query_* equivalents instead.

This should both be more solid and more secure.

We now provide the version as a tagged tuple indicating
whether this is a branch, tag or ref. This should help
rebar automatically upgrade dependencies, and remove
an annoying warning when rebar is used.

In order to detect the type of version the dependencies
must be available, therefore the rebar.config target now
depends on the deps target.

To test this the Cowboy package version had to be changed
from 1.0.4 to master. This is a breaking change, but I do
not expect too many people to still use 1.0.4.

When switching between normal build and running tests
it takes a while for modules to be rebuilt. With the
beam-cache the files are saved and can be restored
when switching between contexts. This greatly speeds
up the context switching.

Instead of calling `find` we use $(wildcard ...) and some
logic on top to find all the files we are looking for.

This is more efficient and greatly helps reduce re-build
times when there's little to be done, particularly when
many dependencies are involved.