Adding support for real kinds with precision up to and including the one specified by the user.

See #386.
Note that for a default compilation, which would now produce real32 and real64 interfaces.
Added interfaces to json_value_module but not yet json_file_module.
Updated the default format statements for reals to account for the specified real kind.

Author: jacobwilliams

src/json_kinds.F90

@@ -59,6 +59,10 @@
 !      integer(kind=int32) [4 bytes]
 #endif
 !      .
+!
+!@note In addition to the real kind specified by `RK`, interfaces for
+!      the real kinds with less precision are also provided in the library,
+!      but all are converted to `real(RK)` variables internally.
 
     module json_kinds
 
@@ -68,6 +72,15 @@ module json_kinds
 
     private
 
+! used for the reals with less precision
+! than the default precision:
+#ifndef REAL32
+    public :: real32
+#endif
+#ifdef REAL128
+    public :: real64
+#endif
+
 #ifdef REAL32
     integer,parameter,public :: RK = real32   !! Default real kind [4 bytes]
 #elif REAL64
@@ -92,7 +105,7 @@ module json_kinds
 
     !*********************************************************
     !>
-    !  Processor dependendant 'DEFAULT' character kind.
+    !  Processor dependent 'DEFAULT' character kind.
     !  This is 1 byte for the Intel and Gfortran compilers.
     integer,parameter,public :: CDK = selected_char_kind('DEFAULT')
     !*********************************************************

src/json_parameters.F90

@@ -64,9 +64,15 @@ module json_parameters
     character(kind=CK,len=*),parameter :: slash           = achar(47, kind=CK) !! JSON special character
     character(kind=CK,len=*),parameter :: backslash       = achar(92, kind=CK) !! JSON special character
 
+    !> default real number format statement (for writing real values to strings and files).
+    !  Note that this can be overridden by calling [[json_initialize]].
+#ifdef REAL32
+    character(kind=CDK,len=*),parameter :: default_real_fmt = '(ss,E17.8E3)'
+#elif REAL128
+    character(kind=CDK,len=*),parameter :: default_real_fmt = '(ss,E46.35E5)'
+#else
     character(kind=CDK,len=*),parameter :: default_real_fmt = '(ss,E27.17E4)'
-        !! default real number format statement (for writing real values to strings and files).
-        !! Note that this can be overridden by calling [[json_initialize]].
+#endif
 
     character(kind=CK,len=*),parameter :: star = CK_'*' !! for invalid numbers and
                                                         !! list-directed real output