Add tags for new failing specs

Author: eregon

spec/tags/core/module/ruby2_keywords_tags.txt

@@ -0,0 +1,8 @@
+fails:Module#ruby2_keywords marks the final hash argument as keyword hash
+fails:Module#ruby2_keywords fixes delegation warnings when calling a method accepting keywords
+fails:Module#ruby2_keywords raises NameError when passed not existing method name
+fails:Module#ruby2_keywords acceps String as well
+fails:Module#ruby2_keywords raises TypeError when passed not Symbol or String
+fails:Module#ruby2_keywords prints warning when a method does not accept argument splat
+fails:Module#ruby2_keywords prints warning when a method accepts keywords
+fails:Module#ruby2_keywords prints warning when a method accepts keyword splat

spec/tags/core/proc/ruby2_keywords_tags.txt

@@ -0,0 +1,6 @@
+fails:Proc#ruby2_keywords marks the final hash argument as keyword hash
+fails:Proc#ruby2_keywords fixes delegation warnings when calling a method accepting keywords
+fails:Proc#ruby2_keywords fixes delegation warnings when calling a proc accepting keywords
+fails:Proc#ruby2_keywords prints warning when a proc does not accept argument splat
+fails:Proc#ruby2_keywords prints warning when a proc accepts keywords
+fails:Proc#ruby2_keywords prints warning when a proc accepts keyword splat

spec/tags/library/matrix/exponent_tags.txt

@@ -0,0 +1 @@
+fails:Matrix#** given an integer _n_ that is 0 returns the identity for square matrices