Updated spectags

* ctags are case-sensitive, and the dataspecs use CamelCase.
* HTML anchor tags are case-sensitive. The old specs used CamelCase to match the
  ctags, and the existing documentation references them extensively.
* reStructuredText links are case-insensitive, and the HTML anchor tags that it
  generates are lower case.

Therefore, the links in the .rst files are given in CamelCase, and the dataspec
formatters convert this to lower case for links. In direct HTML references (in
specs or other areas of documentation), lower case must be used (to be fixed).

Command to generate the file:
cd i2p2www/spec && ctags -f spectags --langdef=rst --langmap=rst:.rst --regex-rst=/_type-\([a-zA-Z0-9]+\)/\\1/t,type/ --regex-rst=/_struct-\([a-zA-Z0-9]+\)/\\1/s,struct/ --regex-rst=/_msg-\([a-zA-Z]+\)/\\1/m,msg/ -R -n *.rst