tutorial: Move method discussion after closures, before generics

/cc: #4217
tutorial: Typos
tutorial: Update for moves based on type

/cc: #4217
tutorial: update intro
tutorial: Fix formatting
tutorial: Remove confusing discussion about semicolons

This takes up a lot of words and isn't very clear. The previous
discussion gets they idea across.

/cc: #4217
tutorial: Remove mutable vector syntax
tutorial: Remove the entire 'Types' section

It's not interesting

/cc: #4217
tutorial: Remove the section on constants

We can mention that constants are declared with 'const' in one line.
Don't need an entire section.
tutorial: Integrate constants into main intro text
tutorial: It doesn't matter that Rust identifiers are the same as C
tutorial: Discuss the primitive types along with their literals
tutorial: Mention rusti with other tools
tutorial: Update scope
tutorial: Fix example in syntax basics section
tutorial: Editing
tutorial: Remove some trivia about operators
tutorial: Try to fit the early discussion of :: in better
tutorial: Clean up language about syntax extensions
tutorial: Typo