Add documentation and change error codes to int

Author: zauguin

README.md

@@ -284,6 +284,7 @@ Errors
 ----
 
 On error, the library throws an error class indicating the type of error. The error classes are derived from the SQLITE3 error names, so if the error code is SQLITE_CONSTRAINT, the error class thrown is sqlite::exceptions::constraint. Note that all errors are derived from sqlite::sqlite_exception and that itself is derived from std::runtime_exception.
+sqlite::sqlite_exception has a get_code() member function to get the SQLITE3 error code.
 
 ```c++
 	database db(":memory:");
@@ -297,7 +298,7 @@ On error, the library throws an error class indicating the type of error. The er
 	/* if you are trying to catch all sqlite related exceptions
 	 * make sure to catch them by reference */
 	catch (sqlite_exception& e) {
-		cerr << e.what() << endl;
+		cerr  << e.get_code() << ": " << e.what() << endl;
 	}
 	/* you can catch specific exceptions as well,
 	   catch(sqlite::exceptions::constraint e) {  } */

hdr/sqlite_modern_cpp.h

@@ -30,11 +30,11 @@ namespace sqlite {
 
 	class sqlite_exception: public std::runtime_error {
 	public:
-		sqlite_exception(const char* msg, char code = -1): runtime_error(msg), code(code) {}
-		sqlite_exception(char code): runtime_error(sqlite3_errstr(code)), code(code) {}
-		char get_code() {return code;}
+		sqlite_exception(const char* msg, int code = -1): runtime_error(msg), code(code) {}
+		sqlite_exception(int code): runtime_error(sqlite3_errstr(code)), code(code) {}
+		int get_code() {return code;}
 	private:
-		char code;
+		int code;
 	};
 
 	namespace exceptions {

tests/exceptions.cc

@@ -17,7 +17,7 @@ int main() {
     // inserting again to produce error
     db << "INSERT INTO person (id,name) VALUES (?,?)" << 1 << "jack";
   } catch (sqlite_exception& e) {
-    cerr << e.what() << endl;
+    cerr << e.get_code() << ": " << e.what() << endl;
     expception_thrown = true;
   } catch (...) {
     cerr << "Ok, we have our excpetion thrown" << endl;