Adds service mode and disable stdin echo

Allows highlight to run continuously while processing input over stdin and output to stdout.

Service mode (--service-mode) is designed to allow several inputs to be parsed on demand from an external application without restarting highlight each time. Service mode runs continuously until a kill signal is sent, EOF is read from STDIN, or the "exit" command is sent instead of a mode line specified below. Service mode expects each input to be separated by a EOF character on a line by itself (if EOF was set to '\0' then "\n\0\n"). Before each file (including the first file) a new mode line must be sent with any mode changes to occur (even if no changes are desired a new line must be sent).

Mode options are changed with key value pairs like option=value separated by a semi colon (no trailing semicolon for last item needed). Any options not changed will retain their previous value. Right now only the following options are supported:

• syntax=<file.ext> to change the syntax to the extension from the filename, or syntax=<syntax_suffix> to set the syntax to use directly (ie csharp).
• tag= if provided and not empty will be printed by itself on a new line to stdout after a file has been processed.
• line-length= set the line length for output wrapping
• eof=<eof_char> A single character (0x00-0xFE) that stdin will contain to separate one file from the next. Recommend 0x00 if you can send it, otherwise 0x01-0x07 are generally easy for most clients to send, ie 0x07 ('\a') for bell. It is near impossible to send several characters above 128 in windows through most term emulators. Note the EOF char must occur on its own new line it cannot be found mid-line. There is no need for a new line between the previous EOF and the next mode options line. You also cannot send the EOF char to new line as it is used as a delimiter already as described.

Finally any file contents can be sent however the file cannot contain the EOF char.

The requirement for the EOF char to be on a line by itself could be altered. It was done that way to have minimal changes to the existed code. For the most part we simply expand current true EOF checks to check for the alternate EOF char.

Also adds disable echo (--disable-echo) for win32 builds to disable console echo back for STDIN. This can be controlled fairly easily in linux with stty if desired by the user, but windows does not have something similar. If we want to expand disable-echo to other platforms that have stty doing

tcgetattr(fileno(stdin), &term);
term.c_lflag &= ~ECHO;
tcsetattr(fileno(stdin), 0, &term);

I can modify if so desired.

Closes #229 (closed)