add temlepete member func in Geo::Point

- Geo::Point#x<ret_type>()
- Geo::Point#y<ret_type>()
- Geo::Point#length<ret_type>()
fix to use cast helper func in Geo::Point class
add temlepete member func in Geo::Line

- Geo::Line#length<ret_type>()
add test case for default constructor

- Geo::Point
- Geo::Line
add test case for degree / radian conversion
Merge pull request #24 from cad-san/fix-geometory-type

add casting helper member func in Geometory Utils