This reverts commit aee21eb0bd.

Fixes #119.

Since Goji accepts the underlying version of this type (i.e., the raw
function), and since it doesn't use web.Handler in the same way as the
net/http ecosystem uses http.Handler, there's really no reason to ever
use web.HandlerFunc.

This is a breaking change. Developers who previously used the
web.HandlerFunc type are encouraged to inline it into their own
projects.

This replaces the enormous free-form docstring at the top with something
that's at least syntax highlighted and collapsible. I'm a little worried
about discoverability, but "oh well."

In order to expose a convenient API, it's unfortunately necessary to
lean on Go's interface{} quite a bit: in reality we only accept a
handful of types at each call site, but it's impossible to express this
using the type system.

Prior to this commit (as well as the ParsePattern commit), I exposed all
of this type information in the form of an enormous comment on web.Mux,
however this was pretty gross. Instead, let's use "vanity" type aliases
for interface{} to provide documentation about which types are accepted
where. This will hopefully make the API documentation easier to skim,
but doesn't affect any existing uses of Goji.

This commit also clarifies a couple other parts of the documentation.

This is a major breaking change to web.C, the Goji context object. The
Env key has been changed from a map[string]interface{} to a
map[interface{}]interface{} in order to better support package-private
environment values and to make the context value more compatible with
golang.org/x/net/context's Context.

Since strings support equality, most existing uses of web.C should
continue to function. Users who construct Env by hand (i.e., by calling
"make") will need to update their code as instructed by their compiler.
Users who iterate over the environment will need to update their code to
take into account the fact that keys may no longer be strings.

Fixing typos and checks

Typo in examples

They say that every programmer builds a web framework at some point. This one is
mine.

The basic idea behind this one is that I wanted a Sinatra for Go, and I couldn't
find one anywhere. Furthermore, net/http is in many ways really close to what I
want out of a Sinatra-in-Go, and many of the frameworks I did find seemed to
reinvent too much, or were incompatible with net/http in weird ways, or used too
much questionable reflection magic. So long story short, I wrote my own.

This implementation is only half-baked, and among other things it's missing a
whole lot of tests.