Add Steve Johnson-style parser recovery rules:

SourceUnit = Error $
    Block = '{' Error '}'
    ContractDefinition = '{' Error '}'
    Statement = Error ';'

Co-Authored-By: chriseth <chris@ethereum.org>

libsolidity/parsing/Parser.h

@@ -41,9 +41,10 @@ class Parser: public langutil::ParserBase
 public:
 	explicit Parser(
 		langutil::ErrorReporter& _errorReporter,
-		langutil::EVMVersion _evmVersion
+		langutil::EVMVersion _evmVersion,
+		bool _errorRecovery = false
 	):
-		ParserBase(_errorReporter),
+		ParserBase(_errorReporter, _errorRecovery),
 		m_evmVersion(_evmVersion)
 	{}