Added `bcrypt-ruby` to Gemfile, pending authentication.

RSpec: 127 examples, 0 failures
Script: 0 tests: 0 failures, 0 errors, 0 pending, 0 omitted
RuboCop: 46 files inspected, no offenses detected
RuboCop global overrides in `.rubocop.yml`: 2
RuboCop local overrides in our source/spec files: 4
Created User table and model; added boilerplate User spec.

This commit also includes an annotated `Blog::Post` model and spec; no
idea why the `annotate` Gem decided to finally wake up and do its thing.

RSpec: 133 examples, 0 failures
Script: 0 tests: 0 failures, 0 errors, 0 pending, 0 omitted
RuboCop: 48 files inspected, no offenses detected
RuboCop global overrides in `.rubocop.yml`: 2
RuboCop local overrides in our source/spec files: 4
Removed method obsoleted in Commit 770ed3b.

RSpec: 133 examples, 0 failures
Script: 0 tests: 0 failures, 0 errors, 0 pending, 0 omitted
RuboCop: 48 files inspected, no offenses detected
RuboCop global overrides in `.rubocop.yml`: 2
RuboCop local overrides in our source/spec files: 4