tests: add lexer tests

Signed-off-by: Marc-Antoine Perennou <Marc-Antoine@Perennou.com>
core: rename reserved_keyword funcs

Signed-off-by: Marc-Antoine Perennou <Marc-Antoine@Perennou.com>
core: define separators API

Signed-off-by: Marc-Antoine Perennou <Marc-Antoine@Perennou.com>
tests: add test-separator

Signed-off-by: Marc-Antoine Perennou <Marc-Antoine@Perennou.com>
implement ku-separator

Signed-off-by: Marc-Antoine Perennou <Marc-Antoine@Perennou.com>