0.5 doc pass

[graydon]

• (DONE) Trait inheritance
• (DONE) Static methods
• (SKIP) Condition macro (this is in the library, likely doesn't belong in manual?)
• (DONE) All noted syntax changes are no longer mentioned
• (DONE) sigil-object types
• (DONE) tuple structs
• (DONE but not committed) enum structs
• (DONE) Drop trait
• (DONE) uniqueness / affineness ("move based on type")
• patterns in function arguments (and do/for block closures)
• (DONE) Struct expressions

[catamorphism]

I'm working on enum structs, but ran into #4229 (which I'm testing a fix for now).