add faceting variable to g_lineplot. add code to maintain factor levels. #20

All 792 tests pass, 33 skipped in 1m 10s

1 files ±0 83 suites ±0 1m 10s ⏱️ +6s
825 tests ±0 792 ✅ ±0 33 💤 ±0 0 ❌ ±0
1 743 runs ±0 1 074 ✅ ±0 669 💤 ±0 0 ❌ ±0

Results for commit 867d907. ± Comparison against earlier commit 3f337dd.