first draft of TECO command documentation generator

 * the language reference is a manually written man-page template
 * containing special references for generated documentation (\#$...)
 * SciTECO script generate-docs.tes extracts TECO comments (/*$ ... */)
   from all source files and transforms them to Troff requests that are
   inserted into the document template.
 * TECO doc comments are a rather sophisticated markup:
   * first part until empty line is called header: simplified command syntax descriptions
   * the rest is called body: <identifier> is automatically underlined,
     empty lines generate new paragraphs, lines beginning with "-" or numbers
     denote an indented unordered or numbered list item.
   * regular Troff requests/macros can be used for more sophisticated markup
   * since Autoconf substitutions are performed on the generated man-page,
     @VARIABLEs@ may be used in doc comments as well
documented generate-docs.tes Troff preprocessor
added option to build manuals as HTML using Groff

 * will be useful for Windows builds since Windows users usally do not have
   a man-page formatter/reader
fixed break-command: without-param it evaluates the search-status
documented commands ending in StateStart
mention sciteco(7) in sciteco(1)
completed documentation of all commands in parser.cpp

 * also updated sciteco(7): add SEE ALSO and AUTHORS
documented remaining commands

 * flow control and other structures have not been documented this ways.
   I have not yet decided whether they should be documented in separate
   sections or use the documentation tool.
outline of remaining language reference
wrote introduction, key translation and immedite editing sections for sciteco(7) manual

 * images are generated by grohtml. they are not listed in the Automake rules but instead all
   sciteco.*.png images are installed and cleaned
elaborate on auto-completions in sciteco(7)
fixed: prevent accessing registers in parse-only mode

 * they might not already exist, yielding bogus errors
 * in case the register might be initialized we do not want to do so in parse-only-mode
 * this fix is only a workaround: currently we must return a register sind got_register() expects one
   and must be called to determine the next state in parse only mode
 * proper solution would be to better separate parsing and execution
prevent image generation during HTML production, instead generate HTML tables using htbl.tes preprocessor
common parent state for all file-name-expecting commands: fixes EM tab-completions

 * StateExpectFile adds no functionality (currently), but is useful for checking state types
generate-docs: marker looks like a Troff request now

it is customary for Troff preprocessors to interpret special preprocessor requests
instead of special comments
manual chapters: Expressions, Command Syntax, Q-Registers
wrote language reference sections about string building and pattern match characters
make success/failure conditional tests more consistent with the definition of success/failure booleans

 * for the S and T conditions, nothing changes effectively (were testing for < 0 already)
 * the F and U conditions were testing for equality to zero which worked for condition booleans
   returned by commands but not for any failure condition (defined as >= 0)
 * may be different in classic TECOs but makes more sense IMHO
written section about flow-control constructs in language reference manual
fixed spelling of Video TECO