Pycfmodel

Additions
- Resolver able to handle AWS SSM values in templates.
Fixes
- Update `CLOUDFORMATION_ACTIONS`

Fixes
- Update `CLOUDFORMATION_ACTIONS`
- `StatementCondition` only builds evaluator if `eval` is called.

Improvements
- Add `StatementCondition` class, with a function resolver as a replacement for `ConditionDict`.
Removes
- Removes constants `CONDITION_MODIFIERS` and `CONDITION_FUNCTIONS` from `pycfmodel/constants.py`
- Removes `is_conditional_dict` from `pycfmodel/utils.py`
Fixes
- Update `CLOUDFORMATION_ACTIONS`
- Change Metadata dict values to accept any type.

Fixes
- Fix to ensure all `Statement.Effect` fields are always capitalized
- Update `CLOUDFORMATION_ACTIONS`

Fixes
- Fix to `policy_documents` method on `EC2 VPC Endpoint` resource type for when no policy document is added to the resource.

Additions
- Add `EC2 VPC Endpoint Policy` resource.
Changes
- Update list of all CloudFormation actions.