Add missing units (#40)

Add celsius, fahrenheit, bar, and the  von Klitzing constant

Author: NoureldinYosri

tunits/core/cython/base_unit_data.pyx

@@ -51,6 +51,8 @@ __SI_BASE_UNITS = [
 __OTHER_BASE_UNITS = [
     BaseUnitData('dB', 'decibel', use_prefixes=False),
     BaseUnitData('dBm', 'decibel-milliwatt', use_prefixes=False),
+    BaseUnitData('degC', 'celsius', use_prefixes=False),
+    BaseUnitData('degF', 'fahrenheit', use_prefixes=False),
 ]
 
 ALL_BASE_UNITS = __SI_BASE_UNITS + __OTHER_BASE_UNITS

tunits/core/cython/derived_unit_data.pyx

@@ -113,6 +113,7 @@ __OTHER_UNITS = [
     DerivedUnitData('ton', None, 'lb', 2000),
     # Pressure.
     DerivedUnitData('psi', 'pounds_per_square_inch', 'Pa', 6894.75729317),
+    DerivedUnitData('bar', 'barometric_pressure', 'Pa', 1e5),
 ]
 
 # Units that aren't technically exact, but close enough for our purposes.

tunits/core/cython/dimension.pyx

@@ -18,13 +18,13 @@ This module creates the dimension abstraction which allows the creation of value
 that belong to a dimension (e.g. t: Time, x: Length, ...etc). This allows us to
 use static types to check code correctness (e.g. time_method(t: Time)).
 
-To add a new dimension, create 3 classes: 
+To add a new dimension, create 3 classes:
 - `class _NewDimension(Dimension):` which implements the abstract methods from
     the abstract `Dimension` class.
 - `class NewDimension(_NewDimension, ValueWithDimension)` which represents scalar
     values and doesn't need to implement any methods.
 - `class AccelerationArray(_Acceleration, ArrayWithDimension)` which represents
-    an array of values sharing the same dimension and 
+    an array of values sharing the same dimension and
 """
 
 import abc
@@ -696,7 +696,11 @@ class _Temperature(Dimension):
     @staticmethod
     @cache
     def valid_base_units() -> tuple[Value, ...]:
-        return (default_unit_database.known_units['kelvin'],)
+        return (
+            default_unit_database.known_units['kelvin'],
+            default_unit_database.known_units['celsius'],
+            default_unit_database.known_units['fahrenheit'],
+        )
 
     def _value_class(self) -> type[Value]:
         return Temperature

tunits/core/cython/physical_constant_data.pyx

@@ -69,6 +69,7 @@ _DERIVED_CONSTANTS = [
     # degrees Rankine
     PhysicalConstantData('degR', None, 5.0 / 9.0, 'K'),
     PhysicalConstantData('bohr_magneton', None, 9.2740096820e-24, 'J/T'),
+    PhysicalConstantData('R_k', 'resistance_quantum', 25812.78277321444, 'ohm'),  # h/e^2
 ]
 
 ALL_PHYSICAL_CONSTANT_DATA = _PHYSICAL_CONSTANTS + _DERIVED_CONSTANTS