[runtime] Add color mode to sgen-grep-binprot.

[runtime] Add color mode to sgen-grep-binprot.

When searching for a pointer with '--color' or '-c', the field in a
protocol entry that matched will be highlighted; when searching for
multiple pointers, they will be highlighted in different colors
according to their order on the command line. When highlighting more
than six pointers, colors will be reused.