exempi for BCR notes

• exempi's directory structure is a bit more complex than other libraries, so it was more readable to put BUILD files throughout the project than have everything done in the root BUILD file.
• The BUILD files generally mimic the Makefile.am files for each directory.
• Note that there are a number of source files for Adobe's new DOM based API that exempi does not yet expose, so these are omitted from the Bazel build.