add postgresql wrapper (#31)

wrapper/Postgresql/README.md

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+Wrapper of IF97 for postgreSQL
+================================================
+
+This wrapper will provide Functions in postgreSQL that provide thermodynamic and transport properties for water/steam at specified state points based on the IAPWS Industrial Formulation for the Properties of Water and Steam.
+
+This wrapper been developed and tested on postgreSQL 9 and 10
+
+------
+
+To Use
+======
+
+* Build the wrapper as a shared lib
+
+* Install .so file into the postgres external module directory (given by pg_config --pkglibdir)  
+
+* run the .sql file to notify you postgreSQL database to use the shared lib
+
+* use provided function : if97_hmass_Tp() and if97_Tsat97() as SQL functions
+
+------
+
+To Build
+========
+
+Follow the build procedures below to create the IF97 module for postgreSQL.
+
+Pre-Requisites
+--------------
+
+* You will need to have postgreSQL *server* installed 
+* You will need g++
+
+Download the IF97 Repository
+----------------------------
+
+* Open a Git window at the drive location where you want to create your local IF97 repository
+
+* Clone the CoolProp/IF97 repository to a local repository (If you haven't already cloned it recursively with CoolProp).::
+
+    git clone https://github.com/CoolProp/IF97
+
+* Change directory (cd) to the IF97 directory you just created.::
+
+    cd IF97
+
+Build and Install
+-----------------------------
+
+* Go to the wrapper/Postgresql directory run `build.sh`
+
+* Connect to your postgreSQL server with your favorite client and execute if97.sql commands

wrapper/Postgresql/build.sh

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+g++ -c -fPIC -Wall -Werror -g3 -O0 -I`pg_config --includedir-server` -I`pg_config --includedir-server`/utils if97.c
+g++ -shared -o if97.so if97.o
+mkdir -p `pg_config --pkglibdir`/if97
+cp ./if97.so `pg_config --pkglibdir`/if97

wrapper/Postgresql/if97.c

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+/*
+ * Filename: if97.c
+ */
+
+ extern "C" {
+    #include <postgres.h>
+    #include <fmgr.h>
+    #include <utils/elog.h>
+    PG_MODULE_MAGIC;
+ }
+
+ #include "../../IF97.h"
+
+ extern "C" {
+     // double hmass(double T, double p)
+     PG_FUNCTION_INFO_V1(if97_hmass_Tp);
+     Datum if97_hmass_Tp(PG_FUNCTION_ARGS) {
+         try {
+             PG_RETURN_FLOAT8(IF97::hmass_Tp(PG_GETARG_FLOAT8(0),PG_GETARG_FLOAT8(1)));
+         } catch (const std::exception& e) {
+            elog(WARNING, "if97: %s",e.what());
+            PG_RETURN_NULL();
+         }
+     }
+
+     // double Tsat97(double p)
+     PG_FUNCTION_INFO_V1(if97_Tsat97);
+     Datum if97_Tsat97(PG_FUNCTION_ARGS) {
+        try {
+            PG_RETURN_FLOAT8(IF97::Tsat97(PG_GETARG_FLOAT8(0)));
+        } catch (const std::exception& e) {
+            elog(WARNING, "if97: %s",e.what());
+            PG_RETURN_NULL();
+        }
+     }
+ }

wrapper/Postgresql/if97.sql

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+CREATE OR REPLACE FUNCTION
+  if97_hmass_Tp(FLOAT8, FLOAT8)
+  RETURNS FLOAT8 AS '$libdir/if97/if97.so', 'if97_hmass_Tp'
+LANGUAGE C WITH ( ISSTRICT );
+
+CREATE OR REPLACE FUNCTION
+  if97_Tsat97(FLOAT8)
+  RETURNS FLOAT8 AS '$libdir/if97/if97.so', 'if97_Tsat97'
+LANGUAGE C WITH ( ISSTRICT );