V1.2

V1.2: Many fixes to the script.

• Updated default bone mappings for easier reference.
• Added aim_matrix_02a + aim_matrix_02b to protected_bones to fix the warnings.
• Stripped out metacarpel bone weight and some messy bone weight steps to avoid stretchy parts.
• Fixed raise Exception — the two mesh validation checks now actually throw instead of silently doing nothing.
• Fixed Spine weight split — REPLACE on spine_0 first before ADD to spine_1, so you get 50/50 not 150/50.
• Fixed list(bones_b) on the removal loop so it doesn't corrupt while iterating.
• Fixed last_direction initialized as 0 (int), not a Vector
  And, some other fixes.