lock protagonist to 0.19.x

[richleland]

Installing api-blueprint-validator fresh right now causes the installation of protagonist 1.0.0. This version appears to require changes to api-blueprint-validator:

Warning: Command failed: /bin/sh -c node ./node_modules/.bin/api-blueprint-validator ./services/introduction.md
.../node_modules/api-blueprint-validator/src/validator.js:74
      result.warnings.forEach(function (warning) {
                     ^
TypeError: Cannot read property 'forEach' of undefined
    at .../node_modules/api-blueprint-validator/src/validator.js:74:22

Aborted due to warnings.

This change locks the version down to 0.19.x, which is a temporary fix until the library can be updated to accommodate any changes made in protagonist.

[cherehapa]

unfortunately we've problem building older protagonist on Ubuntu 14.04 - new protagonist builds if we "apt-get remove node-gyp && npm i -g node-gyp" ( failing on 'node-gyp rebuild' if node-gyp is not replaced w/ newest version via node), but new protagonist is useless due to this forEach bug in master in api-blueprint-validator. Old versions of protagonist specified by ^0.19.3 as in #6 here or locked with =0.19.3 do not build failing on 'node-gyp rebuild'.

[cherehapa]

pull request #16 is a merge of all suggestions, also obsoletes #6