The DEX tool allows "pre-dexing" of library JARs to help reduce build time.
We should investigate how this can be done and what improvements would be seen.
To "pre-dex" a JAR you run the following: `dx --dex --output=lib-dex.jar lib.jar`
The "lib-dex.jar" will contain a "DEX" file containing all the classfiles for that
library JAR. This way when dexing the application dx only needs to merge the
library's DEX file with the other input files (other JARs, classfiles).