adds implementation of `precision` constraint

[desaikd]

Issue #9 #10

Description of changes: This PR works on adding implementation of precision constraint.

Grammar:

<PRECISION> ::= precision: <INT>
              | precision: <RANGE<INT>>

Ion Schema specification: https://amzn.github.io/ion-schema/docs/spec.html#precision

List of changes:

• adds changes to upgrade to v0.10.0 for ion-rs.
• adds Precision enum variants for IslConstraint and Constraint
• adds PrecisionConstraint implementations
• adds changes for validating precision range (Note: precision range must be equal to or greater than 1)
• adds validation logic for precision

Tests: added unit tests for precision implementation.

• adds tests for programmatically creating precision constraint
• adds tests for loading a schema using precision constraint
• adds validation tests for precision constraint