Add wkt parser

What's Changed

• Support wkt format by @alexbol99 in #181

Add function parseWKT(str) to utils to convert single WKT element to flatten-js shape.
Type converted as following
POINT -> Point,
LINESTRING -> Multiline
POLYGON -> Polygon
MULTIPOINT -> Array
MULTILINESTRING -> Array
MULTIPOLYGON -> Polygon
GEOMETRYCOLLECTION -> Array<Point | Multiline | Polygon>

Circular arcs and other types not supported

Full Changelog: v1.5.3...v1.5.5