Update Readme to explain molds

[trinistr]

• Add a big section on molds.
• Improve formatting, change wording a bit.
• Also add Dry::Struct and Point to ease testing.
• Change argument forwarding in Forgeyard to be simpler.

[github-actions]

Coverage after merging document-molds into main will be

99.52%

Coverage Report

File	Stmts	Branches	Funcs	Lines	Uncovered Lines
./lib
object_forge.rb	100%	100%	100%	100%
./lib/object_forge
crucible.rb	100%	100%	100%	100%
forge.rb	100%	100%	100%	100%
forge_dsl.rb	100%	100%	100%	100%
forgeyard.rb	100%	100%	100%	100%
molds.rb	100%	100%	100%	100%
sequence.rb	100%	100%	100%	100%
un_basic_object.rb	90%	100%	100%	90%
./lib/object_forge/molds
hash_mold.rb	100%	100%	100%	100%
keywords_mold.rb	100%	100%	100%	100%
mold_mold.rb	100%	100%	100%	100%
single_argument_mold.rb	100%	100%	100%	100%
struct_mold.rb	93.55%	100%	100%	90.91%
wrapped_mold.rb	100%	100%	100%	100%
./spec
object_forge_spec.rb	100%	100%	100%	100%
./spec/object_forge
crucible_spec.rb	100%	100%	100%	100%
forge_dsl_spec.rb	100%	100%	100%	100%
forge_spec.rb	100%	100%	100%	100%
forgeyard_spec.rb	100%	100%	100%	100%
sequence_spec.rb	100%	100%	100%	100%
un_basic_object_spec.rb	100%	100%	100%	100%
./spec/object_forge/molds
hash_mold_spec.rb	100%	100%	100%	100%
keywords_mold_spec.rb	100%	100%	100%	100%
mold_mold_spec.rb	100%	100%	100%	100%
single_argument_mold_spec.rb	100%	100%	100%	100%
struct_mold_spec.rb	96.36%	100%	100%	96.30%
wrapped_mold_spec.rb	100%	100%	100%	100%
./spec/support
has_an_alias.rb	100%	100%	100%	100%
negated_matchers.rb	100%	100%	100%	100%