Update doxygen docs to be in sync with the README. (#63)

docs/main.dox

@@ -31,9 +31,10 @@ int b = 3;
 KASSERT(a + a == b, "Under the assumption that a is " << a << ", the world is a lie!");
 ```
 
-Use \ref THROWING_KASSERT to throw an exception if the assertion fails. 
-This requires the library to be build in exception mode (`-DKASSERT_EXCEPTION_MODE=On`). 
-If exception mode is not enabled, \ref THROWING_KASSERT acts the same as \ref KASSERT.
+Use \ref THROWING_KASSERT to throw an exception if the assertion fails.
+This requires the target property \c KASSERT_EXCEPTION_MODE to be set
+to \c ON on the target linking against \c kassert. If exception mode is
+not enabled, \ref THROWING_KASSERT acts the same as \ref KASSERT.
 
 ```
 THROWING_KASSERT(1 + 1 == 3, "The world is a lie!");
@@ -51,11 +52,16 @@ argument, followed by the remaining arguments `[, ...]` passed to \ref THROWING_
 
 ### Assertion Levels 
 
-To control which assertions are enabled or disabled, you must supply the CMake option `-DKASSERT_ASSERTION_LEVEL=<numeric>`. 
-If omitted, the assertion level is set to `0`, which disables all assertions. 
+Assertions are enabled if their assertion level (optional third parameter of \ref KASSERT) is <b>less than or equal to</b> the active assertion level.
+The default level is \ref kassert::assert::normal (30).
+Set the CMake target property \c KASSERT_ASSERTION_LEVEL on you target linking against \c kassert to the numeric value of the desired assertion level.
+If omitted, the assertion level is set to 0, which disables all assertions.
 
-Assertions are enabled if their assertion level (optional third parameter of \ref KASSERT ) is **less than or equal to** the active assertion level. 
-The default level is `kassert::assert::normal` (30), see \ref assertion-levels. 
+```cmake
+add_library(my_code ...)
+target_link_libraries(my_code PRIVATE kassert::kassert)
+set_target_properties(my_code PROPERTIES KASSERT_ASSERTION_LEVEL 10)
+```
 
 ### Custom Assertion Levels 
 
@@ -78,7 +84,7 @@ constexpr int heavy = KAMPING_ASSERTION_LEVEL_HEAVY;
 
 ## LICENSE
 
-KAssert is released under the MIT License. See [LICENSE](https://github.com/kamping-site/kassert/blob/main/LICENSE) for details.
+KAssert is released under the MIT License. See ./LICENSE for details.
 
 
   */