[fix/doc] readthedocs missing doxygen definitions

Doxygen definitions for files created by the configure step (like
include/aml/utils/version.h) are not available for documentation on
readthedocs, given that the builder doesn't configure the project before
building the doc.

Replace the version explanation to avoid the use of the affected doxygen
group.

doc/tutorials/hello_world/hello_world.rst

@@ -19,7 +19,30 @@ Setup/Teardown API
 Version API
 ~~~~~~~~~~~
 
-.. doxygengroup:: aml_version
+AML defines its version using semantic versioning, with a macro and variable
+for each subcomponent of the version number:
+
+- **Version major**: denotes ABI changes which prevent compatibility with previous
+  major version ABI.
+- **Version minor**: denotes new features or improvement without breaking the old
+  ABI.
+- **Patch version**: patch and fix releases only.
+
+The full version string is also available directly.
+
+.. code-block:: c
+
+  /* see aml/utils/version.h for details */
+  #define AML_VERSION_MAJOR  ...
+  #define AML_VERSION_MINOR  ...
+  #define AML_VERSION_PATCH  ...
+  #define AML_VERSION_STRING ...
+
+  extern const int aml_version_major    = ...;
+  extern const int aml_version_minor    = ...;
+  extern const int aml_version_patch    = ...;
+  extern const char *aml_version_string = ...;
+
 
 Usage
 -----
@@ -34,7 +57,6 @@ header.
 Initialization is done by passing pointers to the command-line arguments of
 the program to the library.
 
-
 .. code-block:: c
   
   int main(int argc, char **argv){
@@ -44,7 +66,8 @@ the program to the library.
     return 1;
   }
 
-Checking the version is as easy as comparing the header version
+Checking that the program is linked against the same version as the one used
+during compilation is as easy as comparing the header version
 *AML_VERSION_MAJOR* and the library-embedded version *aml_version_major*.
 
 .. code-block:: c