Refactor for ActiveRecord and Config Files

Update Custom Commands to leverage ActiveRecord and save commands to a
database. By default, it will use SQLite. Configuration for this (and
potential configuration for PostgreSQL and MySQL) live in
`config/db.yml`. Inculde a Rakefile for handling DB creation and
migrations.

Rakefile: Add Rakefile to handle running the bot, and DB management
Gemfile: Update with new gem dependencies
db/migrate/*: ActiveRecord migrations for Custom Command
custom_commands.rb: Update to leverage ActiveRecord

Leverage the Rakefile to start the bot, removing the binary file. Update
the Dockerfile to also leverage the Rakefile.

Dockerfile: Update to use Rakefile, and install new dependencies
chronicle: Remove unnecessary start file

Refactor the `chronicle_bot` file into `chronicle` and `matrix`

chronicle.rb: General Chronicle setup
matrix.rb: Start a Matrix-specific bot

Update the bot to read configuration from files, instead of either the
environment, or hard-coded values.

config/db.yml: Database configuration
config/bot.yml: General bot configuration

Update the README to reflect the above change with regards to running
the bot either using the Rakefile, or using a Docker container.

config/bot.yml

@@ -0,0 +1,7 @@
+matrix:
+  homeserver: ''
+  token: ''
+
+log:
+  file: 'chronicle.log'
+  debug: 1

config/db.yml

@@ -0,0 +1,19 @@
+# SQLite Configuration
+adapter:  'sqlite3'
+database: 'db/chronicle-bot.db'
+
+# PostgreSQL Configuration
+# adapter:  'postgresql'
+# database: 'chronicle-bot'
+# host:     'localhost:1234'
+# username: 'chronicle'
+# password: 'ch4ng3m3'
+# encoding: 'utf8'
+
+# MySQL Configuration
+# adapter:  'mysql2'
+# database: 'chronicle-bot'
+# host:     'localhost:1234'
+# username: 'chronicle'
+# password: 'ch4ng3m3'
+# encoding: 'utf8'