Revert "compiler: add !this.elem"

This reverts commit 8165a18039e6c474cf8eb5c391862f1212b1f1dc.
Revert "test: add test for !this.elem"

This reverts commit fec1ceebe2c7cd1f66ca4f49de782d94993b5a78.
compiler: introduce elemMatch

fix #3
0.3.0