Add named regexp resolvers

`ecma` maintains the current behavior of rewriting Ruby's `\A` and `\z`
anchors.
`ruby` uses Ruby's `Regexp` directly.

In the future, I think it may make sense to switch the default to `ruby`
since it's the least surprising behavior. That way people could opt in
to expression rewrites and the rewrites could be more aggressive.

README.md

@@ -113,7 +113,8 @@ JSONSchemer.schema(
   ref_resolver: 'net/http',
 
   # use different method to match regexes
-  # Proc/lambda/respond_to?(:call)
+  # 'ecma'/'ruby'/proc/lambda/respond_to?(:call)
+  # default: 'ecma'
   regexp_resolver: proc do |pattern|
     RE2::Regexp.new(pattern)
   end

lib/json_schemer/schema/base.rb

@@ -30,7 +30,7 @@ def merge(
         :eol => '\z'
       }.freeze
 
-      DEFAULT_REGEXP_RESOLVER = proc do |pattern|
+      ECMA_262_REGEXP_RESOLVER = proc do |pattern|
         Regexp.new(
           Regexp::Scanner.scan(pattern).map do |type, token, text|
             type == :anchor ? RUBY_REGEX_ANCHORS_TO_ECMA_262.fetch(token, text) : text
@@ -53,7 +53,7 @@ def initialize(
         formats: nil,
         keywords: nil,
         ref_resolver: DEFAULT_REF_RESOLVER,
-        regexp_resolver: CachedResolver.new(&DEFAULT_REGEXP_RESOLVER)
+        regexp_resolver: 'ecma'
       )
         raise InvalidSymbolKey, 'schemas must use string keys' if schema.is_a?(Hash) && !schema.empty? && !schema.first.first.is_a?(String)
         @root = schema
@@ -64,7 +64,14 @@ def initialize(
         @formats = formats
         @keywords = keywords
         @ref_resolver = ref_resolver == 'net/http' ? CachedResolver.new(&NET_HTTP_REF_RESOLVER) : ref_resolver
-        @regexp_resolver = regexp_resolver
+        @regexp_resolver = case regexp_resolver
+        when 'ecma'
+          CachedResolver.new(&ECMA_262_REGEXP_RESOLVER)
+        when 'ruby'
+          CachedResolver.new(&Regexp.method(:new))
+        else
+          regexp_resolver
+        end
       end
 
       def valid?(data)

test/json_schemer_test.rb

@@ -933,6 +933,18 @@ def initialize(*args)
     assert_equal(1, new_regexp_class.counts)
   end
 
+  def test_it_allows_named_regexp_resolvers
+    schema = JSONSchemer.schema({ 'pattern' => '^test$' })
+    assert(schema.valid?("test"))
+    refute(schema.valid?("\ntest\n"))
+    schema = JSONSchemer.schema({ 'pattern' => '^test$' }, :regexp_resolver => 'ecma')
+    assert(schema.valid?("test"))
+    refute(schema.valid?("\ntest\n"))
+    schema = JSONSchemer.schema({ 'pattern' => '^test$' }, :regexp_resolver => 'ruby')
+    assert(schema.valid?("test"))
+    assert(schema.valid?("\ntest\n"))
+  end
+
   def test_it_raises_for_invalid_regexp_resolution
     schema = JSONSchemer.schema(
       { 'pattern' => 'whatever' },