fix incomplete pattern matching in `∨` and `∧`
use comprehension for `if-true` for single pass + being more idiomatic
remove `size` as duplicate of `len`; rewrite helper functions in more idiomatic Redex
Checking if a type is bound by a lifetime.

i.e. the lifetime of the type is not shorter than the provided
lifetime.
Merge remote-tracking branch 'philnguyen/master'

Conflicts:
	rust.rkt
Merge pull request #11 from anasazi/fix-ty-bound-by-lifetime

Implement `ty-bound-by-lifetime`
Missing mut annotation in comment.
Added lifetime parameter variance to the syntax.
Function parameters do not have variance.
Account for lifetime variance in subtyping.
Check variance of struct declarations.
Flipped variance of lifetimes in test structs.
&mut T should be invariant in T.
Flip variance of test structs.
Remove trailing whitespace.
Rename subtype-variance to sublifetime.
&'a T is covariant in T not contravariant.
Weakened variance requirements on nested structs.