qsol

Add chapter 2 exercises (2.2.9, 2.2.10, 2.3.1, 2.3.2) and Common polar utilities

Add chapter 2 exercises (2.1–2.2, 2.7) and extend chapter 1 drills

Add exercise_1_2_3 (division 3i/(-1-i)), exercise_1_2_8, exercise_1_1_1, and complex IO programming drill

Merge remote-tracking branch: keep exercise_1_3_4 and add eq_1_49, exercise_1_3_7, exercise_1_3_8

sol