Concatenate, ConcatenateHead, & Filter Assignment Operators

members/lexers/src/assignments/keys.rs

members/lexers/src/assignments/mod.rs

members/lexers/src/assignments/operator.rs

members/lexers/src/assignments/primitive.rs

members/lexers/src/lib.rs

src/lib/parser/assignments/actions.rs

src/lib/parser/assignments/checker.rs

src/lib/parser/assignments/mod.rs

src/lib/parser/assignments/operator.rs

src/lib/parser/assignments/splitter.rs

src/lib/parser/mod.rs

src/lib/parser/statement/functions.rs

src/lib/parser/statement/parse.rs

src/lib/shell/assignments.rs

src/lib/shell/flow_control.rs