Proposed addition on class vs struct

Text is from @hollance's comment in the issue.
Struct-scope constants: More Swift-like?
Remove translations
Changed "closure" to "closure expression" in a few locations

see #35

Note, Closure Expressions create Closures, hence the two terms can be used interchangeably in many instances. Apple does this in their language reference, e.g. they use "trailing closure syntax" rather than "trailing closure expression syntax".

However, there are a few instances in our style guide where I think 'Closure Expression' makes more sense.
Protocol conformance in extensions
Merge pull request #66 from gregheo/translations

No Translations
Merge pull request #67 from ColinEberhardt/master

Changed "closure" to "closure expression" in a few locations
Optional binding, naming and shadowing
Show array enumerate() example
Merge pull request #51 from gregheo/issue-51

new struct inits over old C functions
Merge pull request #58 from gregheo/issue-58

Merge in Matthijs's struct vs classes
Merge pull request #64 from gregheo/64-optional-binding

Variable name for Optional Binding
Merge pull request #70 from gregheo/70-protocol-conformance

Protocol conformance in extensions
Merge pull request #71 from gregheo/array-enumerate-example

Show array enumerate() example
Merge pull request #1 from raywenderlich/master

merge with master