Provide a mechanism to disable imports

[Genarito]

Motivation and proposal

To avoid errors in environments without filesystem access, prevent security problems in sensitive environments, or whatever the reason, each implementation must provide an import disabling mechanism. This flag must be part of the process of parsing a text string in Gura format to a structure useful for the implementation (e.g. a dictionary in Python, an object in Javascript, a HashMap in Java and Rust, etc).

In case the user sets this flag to true it should not be possible to import Gura files into one, and any import statement encountered should throw ImportDisabledError.

This gives more control to the users to use Gura in the most efficient way for their requirements.

Example in Python:

import gura

gura_str = '''
import "some_file.ura"
'''

gura.loads(gura_str, enable_import=False)  # This will throw a ImportDisabledError as imports are disabled

Considerations

• Should we define also how the param should be named?
• Should be a default? Maybe by default is convenient to set it as true to keep portability from Gura 1.0.0 and prevent implicit limitations.

Version

Gura 2.0.0 as It adds breaking changes to the existing API. This change would be introduced with Literal Keys (#10) and new escaped sentences behavior (#11) to prevent a huge amount of versions.

Changes

1. Add ImportDisabledError definition to the Import section.
2. Include changes in a new Changelog section.