cmds/guru: Optimize GuruDefinition command
cmds/guru: Optimize GuruDefinition command

- Use ffjson and pre-generate guru/serial struct

- jump to source use 'edit' instead of 'll'

- Change ByteOffset to line2byte(line('.')) + (col('.')-2)

Signed-off-by: Koichi Shiraishi <13fbd79c3d390e5d6585a21e11ff5ec1970cff0c@zchee.io>

zchee/nvim-go,zchee/nvim-go