Hide large literal values.

Display long strings as:

    "" /* %d byte string literal not displayed */,

See code.google.com/p/go.tools/godoc/static for an example of a long
string literal.

Display the elements of a long composite literal as:

    /* %d elements not displayed */

See github.com/tav/golly/prime for an example of a long composite
literal.
Improve gddo-admin stats command.

- Print header for each section.
- Print truncated packages.
Increase size limit for document truncation.

- Increase size limit from 200000 to 400000.
- Apply the size limit to the compressed size.