test: Add test for GetE().

feat: Add FindAll~().

feat: Add util func()s about a child.

feat: Add logical operation methods.

fix: Each() does't need return val.

feat: Add Each() and EachBreak().

fix: copy() can copy only same length array

fix: Impl Children()

fix: Avoid nil deref of Attr

fix: Avoid nil deref of Attr