faster distinct: maintain seen items in a set

* hy/core/language.hy: maintain the seen items in a set instead of a
  list in `distinct`. This is much faster for lookups.
Merge pull request #494 from theanalyst/fix/distinct

faster distinct: maintain seen items in a set
Making readme more friendly
Merge pull request #499 from sdegutis/patch-1

Making readme more friendly
Implement every? and some
updated import documentation
Merge pull request #503 from rlp10/master

updated import documentation
Merge pull request #501 from microamp/master

Fix issue #498
add @microamp to authors
Introduce scheme flavor of Hy.

As mentioned by @olasd in IRC, hy.flavor.scheme is born.

* hy/flavor/scheme.hy: null? function introduced
* docs/flavor/scheme.rst: Documentation for scheme flavor of Hy
* tests/native_tests/flavor/scheme.hy: Tests for scheme flavor of hy

Signed-off-by: Vasudev Kamath <kamathvasudev@gmail.com>
Fix typo and remove unnecessary progn thanks to @theanalyst

Signed-off-by: Vasudev Kamath <kamathvasudev@gmail.com>
formatting fix for null? documentation

Signed-off-by: Vasudev Kamath <kamathvasudev@gmail.com>
include flavor.scheme tests in __init__.py for native_tests

Signed-off-by: Vasudev Kamath <kamathvasudev@gmail.com>
Add pair? function and fix logic of null? function

* docs/flavor/scheme.rst: Add documentation for pair? function
* hy/flavor/scheme.hy: Fix logic of null? function and add pair?
  function
* tests/native_tests/flavor/scheme.hy: Add tests for pair? function and
  replace assert-true and assert-false with assert statements.

Signed-off-by: Vasudev Kamath <kamathvasudev@gmail.com>