refactor: UNITS_UDLS renamed to UNITS_LITERALS

Also now the existence of the preprocessor flag is enough to trigger the feature (`#ifdef` instead of `#if`)

docs/CHANGELOG.md

@@ -6,7 +6,7 @@
   - (!) refactor: Refactored the library file tree
   - (!) refactor: `quantity::count()` renamed to `quantity::number()`
   - (!) refactor: `data` system renamed to `isq::iec80000` (quantity names renamed too)
-  - (!) refactor: quantity UDLs support has to be enabled with `UNITS_UDLS` preprocessor define
+  - (!) refactor: quantity UDLs support has to be enabled with `UNITS_LITERALS` preprocessor define
   - refactor: quantity (kind) point updated to reflect latest changes to `quantity`
   - refactor: basic concepts, `quantity` and `quantity_cast` refactored
   - refactor: `abs()` definition refactored to be more explicit about the return type

docs/framework/quantities.rst

@@ -87,7 +87,7 @@ User Defined Literals
 Alternatively, to construct quantities with compile-time known values the library provides
 :abbr:`UDL (User Defined Literal)` s for each :term:`unit` of every :term:`dimension`::
 
-    #if UNITS_UDLS
+    #ifdef UNITS_LITERALS
 
     inline namespace literals {
 
@@ -99,11 +99,11 @@ Alternatively, to construct quantities with compile-time known values the librar
 
     }
 
-    #endif // UNITS_UDLS
+    #endif // UNITS_LITERALS
 
 Thanks to them the same code can be as simple as::
 
-    #define UNITS_UDLS 1
+    #define UNITS_LITERALS
 
     using namespace units::isq::si::literals;
     auto d = 123._q_km;     // si::length<si::kilometre, long double>

docs/quick_start.rst

@@ -40,7 +40,7 @@ but still easy to use interface where all unit conversions and dimensional analy
 performed without sacrificing on accuracy. Please see the below example for a quick preview
 of basic library features::
 
-    #define UNITS_UDLS 1
+    #define UNITS_LITERALS
 
     #include <units/format.h>
     #include <units/isq/si/length.h>

docs/usage.rst

@@ -123,8 +123,8 @@ It also runs unit tests during Conan build.
 Conan Options
 ^^^^^^^^^^^^^
 
-udls
-++++
+literals
+++++++++
 
 **Values**: ``True``/``False``
 
@@ -158,14 +158,14 @@ Additionally, enables project documentation generation when the project is being
 CMake Options
 ^^^^^^^^^^^^^
 
-UNITS_UDLS
-+++++++++++++++++++
+UNITS_LITERALS
+++++++++++++++
 
 **Values**: ``ON``/``OFF``
 
 **Defaulted to**: ``OFF``
 
-Equivalent to `udls`_.
+Equivalent to `literals`_.
 
 
 UNITS_DOWNCAST_MODE