Store the version in version.cpp and group the library under src/core

libdpm-core.so's version was reaching the source as a compile-line
definition, with a fallback in two translation units that would have let
the library build and report 0.0.0 if the build ever stopped supplying
it. The version is a literal in src/core/version.cpp, the file named for
it, alongside dpm_core_version() which returns it and the parser for the
X.Y.Z strings modules report.

The library's sources and its version script move to src/core, leaving
src/cli, src/bundled-modules, and the documentation source beside it.

CMakeLists.txt

@@ -8,9 +8,9 @@ set(CMAKE_CXX_STANDARD_REQUIRED ON)
 # libdpm-core.so — the library (C ABI)
 # ---------------------------------------------------------------------
 add_library(dpm-core SHARED
-        src/context.cpp
-        src/modules.cpp
-        src/version.cpp
+        src/core/context.cpp
+        src/core/modules.cpp
+        src/core/version.cpp
 )
 
 target_include_directories(dpm-core PUBLIC
@@ -18,10 +18,6 @@ target_include_directories(dpm-core PUBLIC
         $<INSTALL_INTERFACE:include>
 )
 
-target_compile_definitions(dpm-core PRIVATE
-        DPM_CORE_VERSION_STR="${PROJECT_VERSION}"
-)
-
 # The public C API is the library's entire exported surface; internals
 # stay hidden. The version script pins the export list and versions the
 # symbols.
@@ -30,10 +26,10 @@ target_compile_options(dpm-core PRIVATE
         -fvisibility-inlines-hidden
 )
 target_link_options(dpm-core PRIVATE
-        -Wl,--version-script=${CMAKE_CURRENT_SOURCE_DIR}/src/libdpm-core.map
+        -Wl,--version-script=${CMAKE_CURRENT_SOURCE_DIR}/src/core/libdpm-core.map
 )
 set_property(TARGET dpm-core APPEND PROPERTY
-        LINK_DEPENDS ${CMAKE_CURRENT_SOURCE_DIR}/src/libdpm-core.map
+        LINK_DEPENDS ${CMAKE_CURRENT_SOURCE_DIR}/src/core/libdpm-core.map
 )
 
 target_link_libraries(dpm-core PRIVATE ${CMAKE_DL_LIBS})