[MINOR] Fixed dml-language-reference.md links
[MINOR] Fixed dml-language-reference.md links

There are still links to files that are not present in the docs directory like `files/dml-language-reference/homes.tfspec_bin2.json`

Closes #61.

apache/incubator-systemml,apache/incubator-systemml,apache/incubator-systemml,apache/incubator-systemml,apache/incubator-systemml,apache/incubator-systemml