[ci skip] Document Rails' shifted semver.

* mapper: (34 commits)
  no more is_a checks on instantiation
  Path::Pattern is instantiated internally, so make the contructor require a strexp object
  Strexp#names is only used in a test, so rm
  pass the parsed path from mapper to the Strexp
  add an alternate constructor to Strexp that takes a string
  ask the strexp for the ast
  remove dead code
  disconnect path from the instance
  reuse the ast we already made
  use a parser to extract the group parts from the path
  pass the parsed parameters through the methods so we don't reparse or require caching code
  "controllers" should be a valid path name
  controllers with slash names are also not supported, so we can reuse the message
  only validate controllers
  golf down a bit
  only error handling between controller and action is the same
  add a test for controllers without colons
  move nil check to a method that yields to a block if the value is not nil
  translate action / controller to the desired object
  only one nil check on the action variable
  ...

[ci skip] Include ActiveModel::Model in a class instead of inheriting

require caching code

Don't reference comments that do not exist

Move `type_cast_for_write` behavior over to the serialized type object

Fix broken link in Rails 3.0 release_notes [ci skip]

Refactor serialized types to be partially defined as custom properties

Many of the methods defined in `AttributeMethods::Serialization` can be
refactored onto this type as well, but this is a reasonable small step.
Removes the `Type` class, and the need for `decorate_columns` to handle
serialized types.

* master:
  Update url to rake docs [ci skip]
  Name#model_name doesn't return a String object
  Result sets never override a model's column type
  [ci skip] Make last note show up in postgresql guide.
  Add missing `:param` option from the docs for Mapper#match [ci skip] Option discovered by @zackperdue in #14741, implemented in #5581.
  Add @senny's changed from #14741, including code font for `resources` options, and wrapped to 80 chars. [ci skip]
  Use github url for homepage of log4r [ci skip]
  Remove TODO.
  Ensure we always use instances of the adapter specific column class
  Fix indentation from 1b4b26f1 [ci skip]
  [ci skip] Improve form_helpers.md guide.
  Clear inflections after test.
  Remove unnecessary include for integration tests.
  Added documentation for the :param option for resourceful routing

fixed ActiveModel documentation [ci skip]

Result sets never override a model's column type

MySQL and PostgreSQL provide a column type override in order to properly
type cast computed columns included in a result set. This should never
override the known types of full fledged columns. In addition to messing
up computed properties, this would have led to inconsistent behavior
between a record created with `new`, and a record created with `last` on
the mysql adapter in the following cases:

- `tinyint(1)` with `emulate_booleans` set to `false`
- `text`, `string`, `binary`, and `decimal` columns

Remove unnecessary include for integration tests.

Ensure we always use instances of the adapter specific column class

[ci skip] Make last note show up in postgresql guide.

Option discovered by @zackperdue in #14741, implemented in #5581.