Fixed doc typos in String and Node
Keep empty strings when splitting

To stay consistent with both `String.split/2` and `:binary.split` we
need to keep around empty strings that are accumulated while splitting.
In the future we could support the `:trim` option to consistently remove
these in call calls to `String.split`.

Fixes #1636
String.to_float/1 docs updated
Merge pull request #1644 from jwarwick/string_typos

Fixed doc typos in String and Node
Merge pull request #1645 from vanstee/string-split-repeats

Keep empty strings when splitting