Add link to minitest rdoc & github
[ci skip] Use appropriate mailer syntax.

Reference: https://github.com/rails/rails/commit/f7e4362011ceb1317fd401125d48d7ccb9a1079c
[ci skip] Remove duplicated last! section.

Reference: https://github.com/rails/rails/commit/d4fd0bd17709735ac91e434c94fe99429f078c6e

cc @schneems
Performed Returns true if redirect/render has happened
[ci skip] Normalize all localhost linking.
Fixes small error in ActiveRecord::Reflection docs

[ci skip]
Added Object#self which returns the object itself
Rename Object#self to Object#itself to have parity with matz sanctioned method name for Ruby 2.2
Rename tests too
always return a string from find_script_name

this allows us to avoid nil checks on the return value
just set the host, no need for another hash allocation / merge!
copy edits[ci skip]
Merge branch 'master' of github.com:rails/docrails

Conflicts:
	guides/source/testing.md
Deprecate source_macro

`source_macro` is no longer used in any ActiveRecord code. I've
chosen to deprecate it because it was not marked as nodoc and may
be in use outside of rails source.
rename MiniTest to Minitest
Merge pull request #16373 from eileencodes/deprecate-reflection-source_macro

Deprecate source_macro
Merge pull request #16374 from rajcybage/consistency_minitest

rename MiniTest to Minitest
[ci skip] fix markdown
Merge pull request #16377 from JackDanger/doc-fix-in-association-reflection

Fixes small error in ActiveRecord::Reflection docs
updating documented parameter for build_constraint

Updates documentation in line with changes made in
743b67508e2027e1d086142ccbec47a19fc943f6