avoid using alias in generators

Ruby's alias produces public methods, causing a spurious Thor task
to be created.  For example, this is the reason MigrationGenerator
currently has two tasks:

    > ActiveRecord::Generators::MigrationGenerator.all_tasks.keys
    => ["singular_name", "create_migration_file"]

singular_name was meant to be an attribute, not a task.  Because it's
public, it gets called as a task every time the generator is invoked.

The fix is to ensure all generator methods have the correct
visibility.
Added partial days support to `DateTime`'s `advance` method.

You can now add partial days (e.g. 2.5.days) to `DateTime` with the advance method.
This was acheived by mimicing the `advance` implementation in `Time`.
Fixed changelog
Added documentation for the :param option for resourceful routing
Remove unnecessary include for integration tests.
WIP: pass existing joins to construct_join_dependency
Add documentation for using Rails with a reverse proxy
Merge pull request #13988 from zzak/guides_configuring_reverse_proxy

[Guides] Add documentation for using Rails with a reverse proxy [ci skip]
Merge pull request #9083 from bronson/patch-1

avoid using alias in generators
fixed capitalization
Add FIXME note about the thor bug
Merge pull request #15298 from ShunsukeAida/fix_capitalization

fixed capitalization [ci skip]
rake stats for engines
documentation fix
Merge pull request #15264 from Gaurav2728/gaurav-documentation_fix

documentation link fix and removing unused reader
Merge pull request #15299 from andriytyurnikov/engine_friendly_rake_stats

rake stats for engines
Merge pull request #15210 from arthurnn/fix_hbtm_reflection

Fix habtm reflection
Conflicts:
    activerecord/CHANGELOG.md
    activerecord/lib/active_record/counter_cache.rb
    activerecord/lib/active_record/reflection.rb
    activerecord/test/cases/reflection_test.rb
Use .to_s on _reflections lookup
Skip if the association was already loaded.
Improve readability of Explain Queries table in guides [ci skip]