minor comment improvement
more explanatory comments in some tests
rename vfExec -> ifstack

The variable name vfExec comes from bitcoind, however I find "ifstack" to be a
more explanatory name, and more appropriate for javascript.
add titles to comments for groc

Adding markdown-style titles allow them to show up nicely in the groc
documentation.
fix error and aesthetics of bn comment
put browser bundle above tests in README

...since installing browserify and uglify is necessary to build the bundle
before running the browser tests.
v0.4.0