Stable Release - v1.0.0

1. added type check for dict keys in values
2. converted DictStore class to Singleton using metaclass

• used metaclass to make DictStore act as a singleton
  for a given datastore file path.
• added usage of Path from pathlib to ensure
  both relative and absolute paths are read correctly
  added key type checking and refactored code
• checks for key type and raises KeyError if the key type is
  unsupported.
• moved methods that do not use self to a separate helpers module

3. added test cases to test Singleton behavior
4. fixed issue where FileHandler is unable to create parent directory
5. added Value Type check tests

• refactored tests to create data files in tests/test_data directory

6. updated README.md
7. bump version 0.1.0 -> 1.0.0
8. Move to stable.