Heavily overhaul REML writer and parser.

Major changes to REML parser to:

1. correctly deal with plain text outside of any REML blocks -> such
text is now included in ekBlock blocks.

2. create active text that conforms to the revised document structure
and rules.

REML Writer revised to handle new ekDocument and ekBlock active text
elements. Neither element has any equivalent REML tag. ekDocument is
simply ignored, while active text contained in ekBlock elements is
written out with no surrounding block tag.

Author: delphidabbler