Use not-yet-released version of HSL IO

replace $GLOBALS with \HH\global_get()

hsl-io ^0.2.0, not =0.2.0

Update tests for HSL IO v0.2 (#32)

* Update tests for HSL IO v0.2

I think the logic being tested was bad; there are two classes of issues
here:

- `IO\MemoryHandle` works like a read-write file. `TestLib\StringInput`
  was... unique. Use pipes where we need funky stuff. In particular, if
  it's closed, it can't be read from.

- Checking `isEndOfFile()` before echoing the `> ` prompt was a bug and
  undefined behavior really - consistently prompt before attempting to get
  input

* disable hhast testing temporarily - circular dependency

* Guarantee ordering for '(Before|After)Start'

* comment out full hhast if block

* Require HHVM 4.60

Dependencies need it anyway; even though it's only for dev-depends,
don't want to support a version that can't be tested

Update tests for HSL IO v0.2 (#32)

* Update tests for HSL IO v0.2

I think the logic being tested was bad; there are two classes of issues
here:

- `IO\MemoryHandle` works like a read-write file. `TestLib\StringInput`
  was... unique. Use pipes where we need funky stuff. In particular, if
  it's closed, it can't be read from.

- Checking `isEndOfFile()` before echoing the `> ` prompt was a bug and
  undefined behavior really - consistently prompt before attempting to get
  input

* disable hhast testing temporarily - circular dependency

* Guarantee ordering for '(Before|After)Start'

* comment out full hhast if block

* Require HHVM 4.60

Dependencies need it anyway; even though it's only for dev-depends,
don't want to support a version that can't be tested

permit type-assert v4

Require hsl-io v0.1.0

Experimental change to reduce pain of BC breakages in hsl-experimental

Require hsl-experimental 4.52

Support hsl-experimental < 4.52

Separate release coming soon that requires hsl-experimental 4.52

Fix incaomptible return type for writeAsync in hsl-experimental master