Fix RecursiveAstVisitor (sass#1525)

`visitCalculationExpression` is now properly implemented.

This also adds concrete test classes that extend `RecursiveAstVisitor`
and `RecursiveStatementVisitor` to ensure similar issues are avoided in
the future whenever new AST nodes are added.

Fix RecursiveAstVisitor (sass#1525)

`visitCalculationExpression` is now properly implemented.

This also adds concrete test classes that extend `RecursiveAstVisitor`
and `RecursiveStatementVisitor` to ensure similar issues are avoided in
the future whenever new AST nodes are added.

Add support for the new JS logger API (sass#1515)

See sass/sass#2979

Add support for the new JS logger API (sass#1515)

See sass/sass#2979

Fix interpolation lookahead for calculations (sass#1500)

Closes sass#1499

Fix interpolation lookahead for calculations (sass#1500)

Closes sass#1499

Add back support for min/max calculations (sass#1485)

See sass/sass#3142
See sass/sass#3150

Preserve parentheses around var() functions in calculations (sass#1489)

See sass/sass#3153
See sass/sass#3154

Preserve parentheses around var() functions in calculations (sass#1489)

See sass/sass#3153
See sass/sass#3154

Allow extra whitespace in min, max, and calculations (sass#1483)

Closes sass#1444