Run coveralls on travis

[axic]

Fixes #269.

[axic]

State tests cover 93% of opFns.js: https://coveralls.io/builds/15361640/source?filename=lib%2FopFns.js

[axic]

Fun facts:

• apparently there's no div, mod or mulmod by zero :)
• but there is sdiv and smod by zero
• no sstore overwriting a non-zero value with a non-zero value
• no test with failed create (where the deployment code threw an exception)
• apparently increasing memory is not tested?!
• all precompiles have 100% coverage except modexp (very large inputs are not tested)
• but our coverage test for ecmul/ecadd/ecpairing is unreliable as it uses an external blob (rustbn.js)
• exp only tests 0, 1, 2, 8, 16, 20, 32nd exponent
• data copying (either calldatacopy, codecopy or extcodecopy) doesn't cover unaligned buffers (only ones divisible by the word size of 32)

All the other missing lines are just cases of covering internal exceptions (creating a trie node failed, etc.)

cc @jwasinger @winsvega @pirapira

[axic]

It is also possible to run multiple tests and combine the coverage files (which we should do).

[winsvega]

no sstore overwriting a non-zero value with a non-zero value
this definitely happens in some OOG recursive calls

[holgerd77]

Very cool PR, also remember to add the badge to the README.

[axic]

@holgerd77 should be ok to merge now

[holgerd77]

Great stuff, really looking forward to this.

[holgerd77]

Short note, realized while working on the ethereumjs-devp2p coverage integration: the istanbul package is marked as deprecated and replaced by nyc istanbul CL client.

[pirapira]

@axic do you have the new list of missing test cases? I heard you found some expmod tests for large inputs.

[axic]

Using the "new" (15 days old) tests repo is handled in #272.

Currently it fails on a modexp test case with a large input (gas calculation fails because the bignum exceeds 53bits). We haven't yet fixed the code to see the new coverage figures.

cc @jwasinger @cdetrio