2007-07-26 Major rewrite of mathtext.py, using the TeX box layout model.

There is one (known) backward incompatible change. The

font commands (\cal, \rm, \it, \tt) now behave as TeX does:

they are in effect until the next font change command or

the end of the grouping. Therefore uses of $\cal{R}$

should be changed to ${\cal R}$. Alternatively, you may

use the new LaTeX-style font commands (\mathcal, \mathrm,

\mathit, \mathtt) which do affect the following group,

eg. $\mathcal{R}$.

Other new features include:

- Math may be interspersed with non-math text. Any text

with an even number of $'s (non-escaped) will be sent to

the mathtext parser for layout.

- Sub/superscripts are less likely to accidentally overlap.

- Support for sub/superscripts in either order, eg. $x^i_j$

and $x_j^i$ are equivalent.

- Double sub/superscripts (eg. $x_i_j$) are considered

ambiguous and raise an exception. Use braces to disambiguate.

- $\frac{x}{y}$ can be used for displaying fractions

- $\left(\frac{x}{y}\right)$ may be used to create

parentheses and other delimiters that automatically

resize to the height of their contents.

- Spacing around operators etc. is now generally more like

TeX.

- Added support (and fonts) for boldface (\bf) and

sans-serif (\sf) symbols.

- Log-like function name shortcuts are supported. For

example, $\sin(x)$ may be used instead of ${\rm sin}(x)$

- Limited use of kerning for the easy case (same font)

Behind the scenes, the pyparsing.py module used for doing

the math parsing was updated to the latest stable version

(1.4.6). A lot of duplicate code was refactored out of the

Font classes.

- MGD