move ecdsa test fixtures to end of ecdsa tests

The tests at the start should all be really basic, like testing that an object
can be instantiated. Then come function tests for prototype and static methods.
Then finally the test fixtures.
add minified bundle to browser build

...so one can easily confirm how large the minified version is compared to the
full bundle. Right now, the sizes are:

408195 fullnode.js
245808 fullnode-min.js
642255 tests.js
update readme
update bn.js dependency
test number of ins/outs before pushing
make names easier to recall

"pushin" and "pushout" are a bit confusing. addTxin and addTxout are more
explicit and easier to remember.