Catch up to RST move/rename

Change the make rules for the directory structure.
Update the RST sources which include other RST sources for the
loss of the krb_ prefix.

https://github.com/krb5/krb5/commit/970fc63c63c13a9a15fd0c6dcb6ba7a11ab63c36
Author: Ben Kaduk <kaduk@mit.edu>
Commit: 970fc63c63c13a9a15fd0c6dcb6ba7a11ab63c36
Branch: master
 .gitignore               |    4 +-
 doc/index.rst            |   12 ++++----
 doc/relay/build_this.rst |    8 +++---
 src/doc/Makefile.in      |   62 +++++++++++++++++++++++++++++++---------------
 4 files changed, 54 insertions(+), 32 deletions(-)