generate specific transcoders headers from sources

[ahorek]

fixes

Error:  Failures: 
Error:    TestEConv.testXMLWithCharref:77 array lengths differed, expected.length=43 actual.length=0; arrays first differed at element [0]; expected:<34> but was:<end of array>

because escape tables were changed after: https://github.com/ruby/ruby/commit/ddd9704ae9bf884d867b6f57a16c095a79393fff

autogenerate headers for specific transcoders from ruby sources which should help with future upgrades and prevent mistakes