Amend 'Create a new Page' section of 'Custom Pages' doc
Make rows about 80 chars long
Merge pull request #2511 from AlexVPopov/documentation

Amend 'Create a new Page' section of 'Custom Pages' doc
Amend resource-customization doc
refactor error message for filters
store filters in a hash to simplify implementation

This fixes #2507 and adds tests to ensure that's the case.

When using a hash it's simple to write over an existing filter, and
it's easy to avoid that when adding the default filters in.

Before this commit there was a array of filters that we'd just append,
and later only use the last of for each filter name.
Merge pull request #2515 from Daxter/bugfix/2507-preserve_default_filters!

[2507] Preserve default filters!
update gems where possible (easy)

cucumber & capybara are the hard ones; cucumber-rails is still waiting
on #2388

Gems removed:
sprockets: not needed because Rails itself requires it
guard-coffeescript: not used anywhere
stub! is deprecated; use stub instead
mock & stub are deprecated; use double instead
set up simplecov and make coveralls more accurate

now when you run `rake test` an HTML file is generated by simplecov in
`coverage/index.html` for your perusing pleasure, to see which files
need better coverage
fix wonky problem with minitest & rails 4

see the comments in #2517 for more info
clean up a chunk of the docs
No empty space for hidden fields
convert the README to Markdown :octocat:
remove old / misleading code
:sparkles: