gocctl model v20200819 (#18)

* rename snake、came method

* new: generate model from data source

* add change log md

* update model doc

* update  doc

* beauty code

tools/goctl/model/sql/example/generator.sh

@@ -1,4 +1,7 @@
 #!/bin/bash
 
-# generate usermodel with cache
-goctl model -src ./sql/user.sql -dir ./model -c true
+# generate model with cache from ddl
+ goctl model mysql ddl -src="./sql/user.sql" -dir="./sql/model" -c=true
+
+# generate model with cache from data source
+ goctl model mysql datasource -url="user:password@tcp(127.0.0.1:3306)/database" -table="table1,table2"  -dir="./model"