Add Parsing Code For Scatter-Gather Patterns

[AmirhosseinPoolad]

Adds xml parsing code for scatter-gather patterns, with a sample architecture (That doesn't quite make sense) and test to make sure the code actually runs.

Note that scatter-gather patterns are not implemented in VPR and adding the tag does nothing other than parsing the information in the architecture file.

Information about what scatter-gather patterns and what the tag means is available in the documentation for this PR.

[AmirhosseinPoolad]

To make sure I didn't accidentally break anything else, checked the generated RRGraphs for Titan and Titan-S10 and the diffs were identical other than the very first line with the tool_version attribute. Here's the diff for Titan for example:

diff branch.xml master.xml
1c1
< <rr_graph tool_comment="Generated from arch file stratixiv_arch.timing.xml" tool_name="vpr" tool_version="9.0.0-dev+v9.0.0-1553-g827e72b9c-dirty">
---
> <rr_graph tool_comment="Generated from arch file stratixiv_arch.timing.xml" tool_name="vpr" tool_version="9.0.0-dev+v9.0.0-1558-g6a1fe643f-dirty">