Adding LESS to rake notes

Fixing multi-word automatic inverse detection.

Currently, ActiveRecord models with multiple words cannot have their
inverse associations detected automatically.

Typo Fix[ci skip]

Fix assign ip address with invalid values raise exception

In order that set attribute should not be bang method

Removed redundant asserts for assigns attribute operation

Added SanitizeHelper to rails guide docs [ci skip] 

Generate namespaced routes correctly for generators. Fix for #11532

added String#to_date documentation to Rails 4 upgrade guide [ci skip]

Add description of action in Getting Started Guide [ci skip]

Updated outdated initialization guide [ci skip]

[ci skip]

Closes #11804

using assert_not instead of refute

Add plural form example for AR I18n section [ci skip]

That is a better name, thanks @jeremy.

See the CHANGELONG message in the patch for further details.

Refactor Duration#inspect

In preparing https://github.com/rails/rails/pull/11855, it took me a
minute to understand what was going on due to naming (parts refers first
to an attr_accessor, then to a local, and is then reassigned), but also
because the iterator conditionally builds nulls and then removes them.

I refactored to something much more functional-looking that I find
easier to read, but you may or may not. If you do, great! Enjoy! If
not, oh well, I tried. Can't win 'em all :)

Rationale:

* no name conflict between local var and attr_accessor
* no reassignment of local var
* algorithm spelled out in steps
* unused items in initial list filtered out early
* empty-list case handled early instead of reassigning local var
* no duplication of formatting strings ("0 seconds")

Benchmarks (after PR #11855 merged):

10000.times do
  1.second.inspect
end

original #inspect
   0.350000   0.000000   0.350000 (  0.354709)
   0.330000   0.000000   0.330000 (  0.331885)
   0.330000   0.000000   0.330000 (  0.334441)

refactored #inspect
   0.340000   0.000000   0.340000 (  0.340080)
   0.340000   0.010000   0.350000 (  0.345069)
   0.330000   0.000000   0.330000 (  0.335873)

10000.times do
  (1.day + 1.month + 2.minutes + 1.day).inspect
end

original #inspect
   0.400000   0.000000   0.400000 (  0.403027)
   0.400000   0.000000   0.400000 (  0.403781)
   0.390000   0.000000   0.390000 (  0.387596)

refactored #inspect
   0.400000   0.010000   0.410000 (  0.399792)
   0.400000   0.000000   0.400000 (  0.404145)
   0.400000   0.000000   0.400000 (  0.403820)

Use chop instead of singularize in Duration#inspect

Even though singularize tells a better story, chop is more than 50%
faster and is all that is necessary in the case of Duration#inspect, in
which all of the candidates for chopping appear in the same method and
are all singularized by removing the final 's'.

Benchmarks:

10000.times do
  1.second.inspect
end

original #inspect
   0.740000   0.000000   0.740000 (  0.739065)
   0.740000   0.000000   0.740000 (  0.741458)
   0.740000   0.010000   0.750000 (  0.744011)

refactored #inspect
   0.330000   0.000000   0.330000 (  0.333390)
   0.330000   0.000000   0.330000 (  0.331013)
   0.320000   0.000000   0.320000 (  0.330103)

10000.times do
  (1.day + 1.month + 2.minutes + 1.day).inspect
end

original #inspect
   0.790000   0.000000   0.790000 (  0.794624)
   0.770000   0.000000   0.770000 (  0.774577)
   0.770000   0.010000   0.780000 (  0.771295)

refactored #inspect
   0.390000   0.000000   0.390000 (  0.392921)
   0.400000   0.000000   0.400000 (  0.397412)
   0.370000   0.000000   0.370000 (  0.379660)

Add events reference link to the text about jquery-ujs [ci skip]

Added comment to a guide about necessity of `:dependent` option for asso... [ci skip]

Added comment to a guide about necessity of `:dependent` option for associations with NOT NULL constraint

drop extra variable

Improve #5476 - "Nested attributes with callbacks bugfix" to use add_to_target and clearer tests