coyote: CGCHECKFORSYMBOLS

Description
The purpose of this funciton is to check a string for symbols, encased in escape
characters, that should be revolved with cgSymbol. The cgSymbol name will appear
with the characters "$\" prepended to the name, and the character "$" appended. All
Greek characters and other symbols supported by cgSymbol are allowed. Also,
subscripts and superscripts are allowed::
    $\upTEXT$ : Raise the text in TEXT to superscript level and reduce character size by 62%.
    $\extTEXT$ : Raise the text in TEXT to superscript level and reduce character size by 44%.
    $\downTEXT$ : Lower the text in TEXT to subscript level and reduce character size by 62%.
    $\subTEXT$ : Lower the text in TEXT to subscript level and reduce character size by 44%.
Categories
Utilities
Returns
The modified string with the cgSymbol code embedded in place of the
escaped symbol name.
Params
astring: in, required, type=string
   The string that should be searched for cgSymbol values.
Examples
To create a plot that uses the Greek mu character on the X axis and
the Angstrom squared symbol on the Y axis::
   cgPlot, cgDemoData(1), XTitle='Length ($\mu$M)', YTitle='Distance ($\Angstrom$$\up2$)'
It is possible to use Greek characters as superscripts and subscripts. Do so by
prepending the Greek character with "\\" inside the normal superscript or subscript
notation. For example, to use lambda as an exponent to the Greek character Omega, you
can type this::
   cgPlot, cgDemoData(1), XTitle='$\Omega$$\exp\\lambda$', Charsize=2.0
To use lambda as a subscript, type this:
    cgPlot, cgDemoData(1), XTitle='$\Omega$$\sub\\lambda$', Charsize=2.0
The program has been modified to accept TexToIDL tokens. They must be preceed by
a "\tex" prefix. For example, to draw a right arrow between 5 and 3, you would
construct the embedded string like this::
     aString = '5 $\tex\rightarrow$ 3'
     cgText, 0.5, 0.5, /Normal, Align=0.5, Charsize=3.0, aString
Author
FANNING SOFTWARE CONSULTING::
   David W. Fanning 
   1645 Sheely Drive
   Fort Collins, CO 80526 USA
   Phone: 970-221-0438
   E-mail: david@idlcoyote.com
   Coyote's Guide to IDL Programming: http://www.idlcoyote.com
History
Change History::
   Written by David W. Fanning, 27 July 2012.
   Modified to check for superscript and subscript codes. 9 November 2012. DWF.
   Modified to allow the user to use the TexToIDL program from embedded codes.
       To use a right arrow, for example, aString = '5 $\tex\rightarrow$ 3'
   Added the ability to use Greek letters as subscripts and superscripts. See
       the examples for details. 21 April 2013. DWF.
Copyright
Copyright (c) 2012, Fanning Software Consulting, Inc.