usage: stat.py [Options] [FILE]+
Explanation

    Generates statistics on parse trees. "[FILE]+" is a list of files containing
    serialized parse trees. The format for the parse tree is a pre-order
    enumeration.

    grammar

        nodes := nodes node
        nodes := node
        node := NUM COLON STRING NEWLINE

        COLON = r':'
        NUM = r'[0-9]+'
        STRING = r'.+$'
        NEWLINE = "\\n"

        NB: Whitespace is signficant, but STRING matches whitespace (except for
            newline).

    eg.

        2:root
        2:left side
        0:x
        1:y
        0:z
        3:right side
        0:a
        0:b
        0:c

    corresponds to
                            root
                            /  \
                            /    \
                    left side      right side
                    /    \         /    |    \
                   x      y       a     b     c
                        |
                        z

Options

    -h, help                            print this message
    -v, version                         print the version
    -g, grammar=<file>                  supply a known grammar to annotate
    -o, outdir=<directory>              supply a path to a non-existant
                                        directory
                                        [default: ./gramstats]
    -i, imgs=<bool>                     generate images
                                        [default: true]
    -t, tables=<bool>                   generate statistic tables (as csv files)
                                        [default: true]
    -a, artifacts                       list what artifacts `stat.py` can
                                        generate
    -A, artifact=<artspec>              generate a specific artifact only.
                                        Multiple '-A' flags allowed.
                                        [overrides -o,-i, and -t]
    -T, usetables=<directory>           look for pre-existing statistic tables
                                        in this directory. With this option
                                        no other files are required, however
                                        if more examples are given the tables
                                        are updated. The new tables will only
                                        overwrite the old tables if
                                        "-o <dirname>" == "-T <dirname>"
    -s, stdin                           accept ASTs on standard in. With blank
                                        lines seperating trees. If files are
                                        supplied with this flag it will be an
                                        error.

Specs

    <file>                              the path to a file
    <directory>                         the path to a directory.
    <bool>                              either "true" or "false"
    <artspec>                           <artifact>:<file>
    <artifact>                          an artifact in the list generated by
                                        --artifacts