Merge pull request #55 from mpickering/master

TeX Reader: Improved error messages
TeX reader:  folded escapes int symbols, proper treatment of "\ ".

Previously "\ " was parsed as a symbol " ", now it is parsed as
a medium math space.
TeX reader: Use parsec3 interface.
TeX reader:  Added <??>, improved oneOfCommands, oneOfStrings.

p <??> "string" will attempt the parser p, and if it fails,
return to the starting position before generating the
"expecting string" message.

oneOfStrings (and hence oneOfCommands) now uses this to
improve error messages.
Improved error reporting for environments.
Updated changelog.
Version bump to 0.7.0.1.
Added custom showParseError function.

This uses a caret to indicate the error position.
Fixed mistake in changelog.

The log entry for phantom was a regression, so this as
not a fix relative to 0.7
TeX reader: More accurate position info on certain errors.

parsec's notFollowedBy screws up position info, so we work
around that here.

Example of the input where this matters:  "\ping".
Updated changelog.
Version bump to 0.7.0.2.
Updated cgi demo with install instructions.
Added Text.TeXMath.Readers.OMML.

This is wired into the round-trip tests, but there are not yet
separate tests for the reader.
Version bump to 0.7.1, reflecting new exported module.
OMML: Reader unqualify TeXMath types

We don't have to worry about collisions anymore.
First stab at intepreting string types.
OMML: improve grouping.
Move Exp-processing functions to Shared.

These aren't specific to MathML.
Fix one more String-processing part.