Replace watchr with Guard

watchr has not been maintained for quite some time and no longer works
properly with Ruby 2.2.

Gemfile

@@ -12,4 +12,5 @@ gem 'rspec-expectations', '>= 3.2.0', '< 4'
 gem 'yard'
 gem 'redcarpet'
 gem 'pygments.rb'
-gem 'watchr'
+gem 'guard'
+gem 'guard-yard'

Gemfile.lock

@@ -14,26 +14,57 @@ GEM
       bundler
       rake
       thor (>= 0.14.0)
+    celluloid (0.16.0)
+      timers (~> 4.0.0)
     coderay (1.1.0)
     diff-lcs (1.2.5)
+    ffi (1.9.8)
+    formatador (0.2.5)
+    guard (2.12.5)
+      formatador (>= 0.2.4)
+      listen (~> 2.7)
+      lumberjack (~> 1.0)
+      nenv (~> 0.1)
+      notiffany (~> 0.0)
+      pry (>= 0.9.12)
+      shellany (~> 0.0)
+      thor (>= 0.18.1)
+    guard-yard (2.1.4)
+      guard (>= 1.1.0)
+      yard (>= 0.7.0)
+    hitimes (1.2.2)
+    listen (2.10.0)
+      celluloid (~> 0.16.0)
+      rb-fsevent (>= 0.9.3)
+      rb-inotify (>= 0.9)
+    lumberjack (1.0.9)
     method_source (0.8.2)
+    nenv (0.2.0)
+    notiffany (0.0.6)
+      nenv (~> 0.1)
+      shellany (~> 0.0)
     posix-spawn (0.3.8)
     pry-nav (0.2.4)
       pry (>= 0.9.10, < 0.11.0)
     pygments.rb (0.3.7)
       posix-spawn (~> 0.3.6)
       yajl-ruby (~> 1.1.0)
     rake (10.4.2)
+    rb-fsevent (0.9.4)
+    rb-inotify (0.9.5)
+      ffi (>= 0.5.0)
     redcarpet (3.0.0)
     rspec-core (3.2.0)
       rspec-support (~> 3.2.0)
     rspec-expectations (3.2.0)
       diff-lcs (>= 1.2.0, < 2.0)
       rspec-support (~> 3.2.0)
     rspec-support (3.2.1)
+    shellany (0.0.1)
     slop (3.6.0)
     thor (0.19.1)
-    watchr (0.7)
+    timers (4.0.1)
+      hitimes
     yajl-ruby (1.1.0)
     yard (0.8.7.3)
 
@@ -43,12 +74,13 @@ PLATFORMS
 DEPENDENCIES
   appraisal (~> 1.0)
   bundler (~> 1.1)
+  guard
+  guard-yard
   pry!
   pry-nav
   pygments.rb
   rake (~> 10.0)
   redcarpet
   rspec-core (>= 3.2.0, < 4)
   rspec-expectations (>= 3.2.0, < 4)
-  watchr
   yard

Guardfile

@@ -0,0 +1,5 @@
+guard 'yard' do
+  watch('README.md')
+  watch(%r{doc_config/yard/.+})
+  watch(%r{lib/[^/]+\.rb})
+end