[Feature]: Add IOS XR Factory parsing

[mpenning]

IOS XR uses different syntax and there needs to be a unique syntax="iosxr" keyword; one example: Github Issue #291

Add a syntax="iosxr" keyword and initial factory parsing for IOS XR.

Raise an error until syntax="iosxr" is viable.

[github-actions[bot]]

This issue has automatically been marked stale due to inactivity. The issue will close unless further activity occurs. Please understand that the CiscoConfParse team is not obligated to comment on every issue. For more detailed information, please refer to our CONTRIBUTING guidance -> https://github.com/mpenning/ciscoconfparse/blob/main/.github/CONTRIBUTING.md

[github-actions[bot]]

This issue has automatically been marked stale due to inactivity. The issue will close unless further activity occurs. Please understand that the CiscoConfParse team is not obligated to comment on every issue. For more detailed information, please refer to our CONTRIBUTING guidance -> https://github.com/mpenning/ciscoconfparse/blob/main/.github/CONTRIBUTING.md

[github-actions[bot]]

Due to inactivity, CiscoConfParse's maintainers are closing this issue. Please refrain from further comments. In the future, CiscoConfParse's maintainers may reopen it solely at their own discretion. For more detailed information, please refer to our CONTRIBUTING guidance -> https://github.com/mpenning/ciscoconfparse/blob/main/.github/CONTRIBUTING.md