BUG: Table.copy did not retaing table.type

This would cause copies of a table to not be equal when compared using
the __eq__ method.
DOC: Add note to ChangeLog.md

[skip ci]
Merge pull request #494 from ElDeveloper/copy-didnt-retain-table-type

BUG: Table.copy did not retaing table.type
Merge branch 'master' of github.com:biocore/biom-format into issue_492

Conflicts:
	ChangeLog.md