Pyfixest 018 (#358)

* prepare 018 release

* lint

* fix bugs, allow var2 to be int, fix docs

* model_matrix_fixest now returns dict instead of tuple

.gitignore

@@ -21,4 +21,3 @@ readme.ipynb
 #objects.json
 #docs/site_libs
 #site_libs
-

docs/news.qmd

@@ -2,7 +2,12 @@
 
 ## PyFixest 0.18.0
 
-- Large Refactoring of Interal Processing of Model Formulas, in particular `FixestFormulaParser` and `model_matrix_fixest`.
+- Large Refactoring of Interal Processing of Model Formulas, in particular `FixestFormulaParser` and `model_matrix_fixest`. As a results, the code should be cleaner and more robust.
+- The `fml` argument of `model_matrix_fixest` is deprecated. Instead, `model_matrix_fixest`
+  now asks for a `FixestFormula`, which is essentially a dictionary with information on model
+  specifications like a first stage formula (if applicable), dependent variables, fixed effects,
+  etc.
+- Additionally, `model_matrix_fixest` now returns a dictionary instead of a tuple.
 - Brings back fixed effects reference setting via `i(var1, var2, ref)` syntax. Deprecates the `i_ref1`, `i_ref2` function arguments.
 
 ## PyFixest 0.17.0