* Allow multiple independent context stacks per thread

* Renames RuntimeContext to RuntimeContextWrapper
* Each stack item is aware of its wrapper and is able to pop itself
* Push base context on initialisation for every wrapper so that one is always inside a context
* Adds push_context and pop_context methods on RuntimeContextWrapper to simplify access when "with" syntax is not convenient
* Bump version: 2.0.0 → 3.0.0

* Backwards incompatible rename of context_var_updated to context_var…

…_set -- also, it is no longer triggered on context exit

* New event context_var_reset which is triggered on context exit
* Adds individual context var reset method and delattr functionality on both RuntimeContext and EnvBase

* Bump version: 1.3.0 → 2.0.0

* Fixes dictionary modification while iteration in context_var_update…

…d handling if that involved setting vars

* Adds RuntimeContext.reset_context
* Adds EnvBase.reset_context
* Examples

* Bump version: 1.2.2 → 1.3.0

Add EnvBase to exports

Bump version: 1.2.1 → 1.2.2

Fixes hookery version spec

Bump version: 1.2.0 → 1.2.1

* Updated for hookery v2 to allow simpler listening to individual con…

…text var changes

* Allow setting runtime context vars by setting attributes on runtime context
* Bump version: 1.1.0 → 1.2.0

* Allow listening to context var updates via Env.context_var_updated …

…hook

* RuntimeContext.context_entered and RuntimeContext.context_exited event handlers now get context_vars instead of rather pointless runtime_context reference

* Bump version: 1.0.0 → 1.1.0

* Simplified rewrite of env

* Bump version: 0.5.0 → 1.0.0

* RuntimeContextEnv cannot be strictly strict because user may still …

…want to set instance attributes on their custom Env class. This removes the impractical strictness.

* Adds tox.sh script
* Bump version: 0.4.1 → 0.5.0

travis.yml