Converts a set of FILEs into the Ur/Web modules. Each Module will contain
  following functions:

    val binary : unit -> transaction blob
    val blobpage : unit -> transaction page
    val text : unit -> transaction string

    Additionally, FFI signatures will be provided for JavaScript files. In order
    to enable this, you have to name your JS functions using the name__type
    scheme. See README for details. Also, uru project uses this a lot.

    (NOTE: the interface is not stable. Pleas, fork the Urembed sources
    before using)

  The master project (specified with -o FILE.urp) will contain a dictionary
  version of those functions taking the datatype key as an argument, instead of
  unit. In order to actually compile the binaries, you have to call

    make -f FILE.mk CC=.. LD=.. UR_INCLUDE_DIR=.. urp

  Where FILE.mk is the Makefile, generated by urembed.

    Example: urembed -o static/Static.urp Style.css Script.js
             make -C static -f Static.mk CC=gcc LD=ld UR_INCLUDE_DIR=/usr/local/include/urweb urp

  Note: output directory should exist