Improve Enum basics section (#534)
Improve Enum basics section (#534)

* Improve Enum basics section
This includes:
- several additions to examine functions and enumerate over them
- a dive into built in documentation with some helpers
The reasoning here originally started when I wanted to double-check the
accuracy of the count of functions that was listed.
Running

```
Enum.__info___(:functions) |> Enum.count
```

yields `82`, which is less than 100, so I clarified the language.
But then I realized some of the other tidbits I could do now that I had
a list of functions and their arity via the __info__ call, which led to
the changes seen.

* update RE @doomspork review feedback after far too long

* Clarify language after added initial section examining the Enum modules functions

* vas --> vast in enum basics

huydx/elixir-school,ElixirVietnam/elixir-school,yuriibodarev/elixir-school,doomspork/elixir_school,erickgnavar/elixir-school,doomspork/elixir-school,nscyclone/elixir-school,nscyclone/elixir-school,ElixirVietnam/elixir-school,doomspork/elixir_school,ElixirVietnam/elixir-school,doomspork/elixir_school,doomspork/elixir-school,erickgnavar/elixir-school,huydx/elixir-school,huydx/elixir-school,yuriibodarev/elixir-school,psantos10/elixir-school,yuriibodarev/elixir-school,nscyclone/elixir-school,nscyclone/elixir-school,doomspork/elixir-school,erickgnavar/elixir-school,psantos10/elixir-school,psantos10/elixir-school