use "compilation" instead of "optimization"

relevant since it also refers to USE_TIMINGOUTPUT etc.

CMakeLists.txt

@@ -85,7 +85,7 @@ list(APPEND TURTLE_LIBS "${OpenMP_CXX_LIB_NAMES}")
 #####################################################################################
 ## Extra flags
 
-set(CMAKE_CXX_COMPILE_FLAGS "${CMAKE_CXX_COMPILE_FLAGS} $ENV{TURTLE_OPTIMIZATION_FLAGS} -Wall -g")
+set(CMAKE_CXX_COMPILE_FLAGS "${CMAKE_CXX_COMPILE_FLAGS} $ENV{TURTLE_COMPILATION_FLAGS} -Wall -g")
 set(CMAKE_CXX_FLAGS "${CMAKE_CXX_FLAGS} ${CMAKE_CXX_COMPILE_FLAGS}")
 
 #####################################################################################

README.rst

@@ -126,7 +126,7 @@ Detailed full installation instructions:
      * `HDF5_ROOT`            - Base directory of HDF5
      * `CMAKE_PREFIX_PATH`    - Directory containing local cmake configuration files
 
-    We also recommend that an environment variable `TURTLE_OPTIMIZATION_FLAGS`
+    We also recommend that an environment variable `TURTLE_COMPILATION_FLAGS`
     is defined appropriately.
     In particular, for clusters of unknown architecture it helps to log into
     individual nodes and run the following command: