Update README to reflect file reorganization
Add shortcuts to common preamble

This commit adds a lot of unicode shortcuts to the common preamble,
other commits will make these changes in the LaTeX documents.
Convert asymptotics doc to unicode

A hopefully comprehensive conversion of LaTeX code to unicode
characters wherever possible in the asymptotics files.  This change
should make the source code easier to read.
Convert LaTeX characters to unicode in linear regression doc

Another (hopefully comprehensive) attempt to improve the
source code readability by converting LaTeX to unicode
wherever possible.
Convert LaTeX to unicode in finitesample docs

A last readability improvement by converting LaTeX characters
to unicode.
Convert LaTeX to unicode in probability document

One more attempt to improve source-code readability by converting
LaTeX characters to unicode.