Remove path from index

[bkille]

• PAF path is no longer stored as part of the *.impg index. This means that this PR will be incompatible with any index created by an earlier version
• Removed CLI arguments which allowed custom index paths. The index for a PAF file path/to/aln.paf will always be path/to/aln.paf.impg, similar to .fai indices for FASTA files.
• Updated the version number to v0.2.0, since this breaks previous indices.
• Added rule to GitHub CI to run tests on all PRs (can make this a separate branch if desired)