Add more actions for the front-end

[emi2k01]

Right now there's

• open_file <file> opens file
• highlight_regex <file> <from> <to> opens file and highlights the lines starting from the line containing from and ending in the line containing to

But there are other actions that might be useful like

• highlight_one <file> <pattern> opens file and highlights the first match of pattern
• highlight_all <file> <pattern> opens file and highlight all the matches of pattern
• go_to_page <page> goes to the page whose file name matches page (or maybe the title that matches )

I'd also like to rename highlight_regex to highlight_lines