Add basic rubocop configuraton for Hound

This way we can ask contributors to follow some basic guidelines like
removing trailing whitespaces while not overwhelming them with all our
rules.

.hound.yml

@@ -0,0 +1,2 @@
+rubocop:
+  config_file: .rubocop_basic.yml

.rubocop.yml

@@ -1,35 +1,8 @@
-require: rubocop-rspec
-
-AllCops:
-  DisplayCopNames: true
-  DisplayStyleGuide: true
-  Include:
-    - '**/Rakefile'
-    - '**/config.ru'
-  Exclude:
-    - 'db/**/*'
-    - 'config/**/*'
-    - 'script/**/*'
-  TargetRubyVersion: 2.3
-  # RuboCop has a bunch of cops enabled by default. This setting tells RuboCop
-  # to ignore them, so only the ones explicitly set in this file are enabled.
-  DisabledByDefault: true
+inherit_from: .rubocop_basic.yml
 
 Metrics/LineLength:
   Max: 100
 
-Layout/IndentationConsistency:
-  EnforcedStyle: rails
-
-Layout/EndOfLine:
-  EnforcedStyle: lf
-
-Layout/TrailingBlankLines:
-  Enabled: true
-
-Layout/TrailingWhitespace:
-  Enabled: true
-
 Bundler/DuplicatedGem:
   Enabled: true
 

.rubocop_basic.yml

@@ -0,0 +1,28 @@
+require: rubocop-rspec
+
+AllCops:
+  DisplayCopNames: true
+  DisplayStyleGuide: true
+  Include:
+    - '**/Rakefile'
+    - '**/config.ru'
+  Exclude:
+    - 'db/**/*'
+    - 'config/**/*'
+    - 'script/**/*'
+  TargetRubyVersion: 2.3
+  # RuboCop has a bunch of cops enabled by default. This setting tells RuboCop
+  # to ignore them, so only the ones explicitly set in this file are enabled.
+  DisabledByDefault: true
+
+Layout/IndentationConsistency:
+  EnforcedStyle: rails
+
+Layout/EndOfLine:
+  EnforcedStyle: lf
+
+Layout/TrailingBlankLines:
+  Enabled: true
+
+Layout/TrailingWhitespace:
+  Enabled: true