Fix Obj texture parsing error: where obj texture map statement contains texture option, it will fail to parse the correct image url, as a result, the texture won't be shown. Besides, we also add clamp texture mode for obj
refactor the code, also  parse texture option explictly
Merge pull request #204 from zhgw01/zhgw01/FixObjTextureUrl

Fix Issue #201: When Obj texture map statement contains texture option, assimp will fail to import texture