Makes few cleanning and adds an obi_dms C constructor

src/obidms.h

@@ -61,6 +61,23 @@ typedef struct OBIDMS {
                                      */
 /**@}*/
 
+/*@
+ * @brief Check if a OBIDMS exist
+ *
+ * @param name a pointer to a C string containing the name of the database
+ *             the actual directory name used to store the DMS will be
+ *             `<name>.obidms`
+ *
+ * @return an integer value indicating the status of the database
+ * @retvalue 1 the database exist
+ * @retvalue 0 the database does not exist
+ * @retvalue -1 an error occurs
+ *
+ * @see obi_close_dms()
+ * @since May 2015
+ * @author Eric Coissac (eric.coissac@metabarcoding.org)
+ */
+int obi_dms_exists(const char* name);
 
 /**
  * @brief Create a new OBITools Data Management instance (OBIDMS).
@@ -108,6 +125,29 @@ OBIDMS_p obi_create_dms(const char *name);
  */
 OBIDMS_p obi_open_dms(const char *name);
 
+/**
+ * @brief Create a new OBIDMS instance.
+ *
+ * If the database already exist this function open it, otherwise it
+ * creates a new databse.
+ *
+ * @param name a pointer to a C string containing the name of the database
+ *             the actual directory name used to store the DMS is
+ *             `<name>.obidms`
+ *
+ * @return a pointer to an OBIDMS structure describing the newly created DMS
+ * @retval NULL on error and the `obi_errno`variable is set.
+ *
+ * ###Error values
+ * 		- OBIDMS_LONG_NAME_ERROR : the database name exceeds the limit.
+ * 		- OBIDMS_MEMORY_ERROR    : something wrong occurs during memory allocation.
+ *
+ * @see obi_close_dms()
+ * @since May 2015
+ * @author Eric Coissac (eric.coissac@metabarcoding.org)
+ */
+OBIDMS_p obi_dms(const char *name);
+
 /**
  * @brief Close an opened OBITools Data Management instance (OBIDMS).
  *