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
Fixed a problem where `sum`, `size`, `average`, `minimum` and `maximum` used
with a grouping was not returning a Hash.
WIP: pass existing joins to construct_join_dependency
Move PG OID types to their own files

As we promote these classes to first class concepts, these classes are
starting to gain enough behavior to warrant being moved into their own
files. Many of them will become quite large as we move additional
behavior to the type objects.
Move extract_scale to decimal type

The only type that has a scale is decimal. There's a special case where
decimal columns with 0 scale are type cast to integers if the scale is
not specified. Appears to only affect schema dumping.
we can just use Ruby here
remove dead code. @klass isn't used anymore
use the existing constant rather than the hardcoded string

so tht I don't go totally insane with THsi crazy hash driven
development. why is Everything a hash? Why do people think hashes in
hashes with random keys is a Good API? You can't find things or
deprecate them or control access whatsoever, you just have to hope that
everyone is like "oh, you want to change that? that's cool! we all know
it's hashes so go for it!"

The End.
middle variable is never used, so rm
fewer object allocations and method calls during route match
drop hash allocations during match
Merge pull request #15218 from sgrif/sg-move-oid-types

Move PG OID types to their own files
Merge pull request #15237 from sgrif/sg-move-extract-scale

Move extract_scale to decimal type
Rename Posts to Articles in Guides, continuation of 2d446e77 / #13774 [ci skip]
Merge pull request #15215 from JohnKellyFerguson/rename-posts-to-articles

Documentation: Rename Posts to Articles
Update CHANGELOG.md

Most recent change should be moved to the top
Merge pull request #14803 from kuldeepaggarwal/null_relation_sum_fix

Fixed a problem where `sum` used with a `group` was not returning a Hash.
Form full URI as string to be parsed in Rack::Test.

There are performance gains to be made by avoiding URI setter methods.