Add note to Enum to clarify what's returned

In particular clarify that infinite streams don't work with many of the
functions.
Merge pull request #1662 from pminten/note-about-enum-list-return

Add note to Enum to clarify what's returned
Improve Enum docs
out of it -> as result
Make a distinction about eager and full evaluation of the collection
Fix Stream.take/2 and Stream.take_while/2 for Stream.Lazy
Markdown rendering fix
adding tests for ipv6 addresses on URIs
handling IPv6 addresses on URIs

* very naïve and permissive regex to check for IPv6 addreses.
Merge pull request #1668 from elia/doc-fix

Markdown rendering fix
Merge pull request #1667 from betawaffle/lazy-throw-fix

Fix Stream.take/2 and Stream.take_while/2 for Stream.Lazy
Consider stream_lazy to always return the result, move nesting check to after reduce
more tests for IPv6
No longer trim by default when splitting

Further discussion here:

  https://groups.google.com/forum/#!topic/elixir-lang-core/66gb3J0bnUA
Return error on unsupported options in Regex.compile
parsing embedded IPv4 addresses
Merge pull request #1669 from brunoro/ipv6-uri

URI.parse supports IPv6 addresses
Merge pull request #1672 from meh/regex-compile

Return error on unsupported options in Regex.compile
Merge pull request #1671 from vanstee/string-split-trim-default

No longer trim by default when splitting
Support negative indicies in Enum.at/fetch/fetch!