Full support of English documents

Change the YaTeX-math-mode's prefix from `,' to `;'. ...

Add YaTeX-apropos, YaTeX-what-column, YaTeX-beginning-of-environment,
YaTeX-end-of-environment.
Add variables YaTeX-default-pop-window-height, YaTeX-close-paren-always,
YaTeX-no-begend-shortcut, YaTeX-auto-math-mode.
Remove Greek letters from maketitle-type.
Make YaTeX-inner-environment two times faster and more reliable.
C-u for [prefix] k kills contents too.
Fix the detection of the range of section-type commands when nested.
Add \end{ completion.
Add YaTeX-generate-simple.
Refine documents(using Texinfo).
%#REQUIRE for sub-preambles.