Define `log1p` and `expm1` as acting on OP-chains

Amend the operator section as well to make both functions also work on
chains of operators.

nifty6/operators/operator.py

@@ -158,8 +158,8 @@ class Operator(metaclass=NiftyMeta):
         return None, self
 
 
-for f in ["sqrt", "exp", "log", "tanh", "sigmoid", 'sin', 'cos', 'tan',
-          'sinh', 'cosh', 'absolute', 'sinc', 'one_over', 'log10']:
+for f in ["sqrt", "exp", "log", "sin", "cos", "tan", "sinh", "cosh", "tanh",
+          "sinc", "sigmoid", "absolute", "one_over", "log10", "log1p", "expm1"]:
     def func(f):
         def func2(self):
             fa = _FunctionApplier(self.target, f)

test/test_field.py

@@ -335,7 +335,7 @@ def test_emptydomain():
 @pmp('dom', [ift.RGSpace((8,), harmonic=True), ()])
 @pmp('func', [
     "exp", "log", "sin", "cos", "tan", "sinh", "cosh", "sinc", "absolute",
-    "sign", "log10"
+    "sign", "log10", "log1p", "expm1"
 ])
 def test_funcs(num, dom, func):
     num = 5