Reassurance Elbow Suite

We have another patch level release ready that lets libsass rock even more 🎸
This release mainly fixes output issues related to lists, numbers and interpolations 🪲
Totally 17 issues fixed with 16 pull requests and 26 new unique passing spec tests 🍻

Bugfixes

• Normalize numbers after operations (@mgreter, #1163, #1164)
• Force evaluation of binary expression in interpolation (@mgreter, #1162, #1165)
• Fix precision output format for numbers (@mgreter, #1153, #1166)
• Implement missing unit groups conversions (@mgreter, #1167, #1172)
• Fix append function when handling argument lists (@mgreter, #1171, #1173)
• Fix interpolation escape sequence edge case (@mgreter, #1168, #1174)
• Fix edge case with parent selector evaluation (@mgreter, #1170, #1176)
• Implement correct String Schema parsing (@mgreter, #1158, #1177)
• Fix a few list output edge cases (@mgreter, #1178, #1179)
• Add error message for empty interpolations (@mgreter, #1093, #1180)
• Fix white-space error with nested output style (@mgreter, #1092, #1181)
• Fix some compiler warnings (@mgreter, #1117, #1182)
• Fix parent selector interpolation in attribute selector (@mgreter, #1016, #1183)
• Fix String_Schema and Binary_Expression parsing (@mgreter, #948, #1177)