conn/physic: redo the package that was added in 0bc4d173ac

It realized I did it wrong. Decouple and disambiguate the 'measurement type'
from the 'unit used'.

While trying to micro-optimize for 32 bits architecture, I missed the greater
picture. Use int64 for most types.

Include 100% test coverage and examples.

devices/units.go

@@ -10,7 +10,7 @@ import (
 
 // Milli is a fixed point value with 0.001 precision.
 //
-// Deprecated: This interface will be removed in v3. Use physic.Milli instead.
+// Deprecated: This interface will be removed in v3.
 type Milli int32
 
 // Float64 returns the value as float64 with 0.001 precision.
@@ -29,7 +29,7 @@ func (m Milli) String() string {
 
 // Celsius is a temperature at a precision of 0.001°C.
 //
-// Deprecated: This interface will be removed in v3. Use physic.Celsius
+// Deprecated: This interface will be removed in v3. Use physic.Temperature
 // instead.
 type Celsius Milli
 
@@ -50,7 +50,7 @@ func (c Celsius) ToF() Fahrenheit {
 
 // Fahrenheit is an unsound unit used in the United States.
 //
-// Deprecated: This interface will be removed in v3. Use physic.Fahrenheit
+// Deprecated: This interface will be removed in v3. Use physic.Temperature
 // instead.
 type Fahrenheit Milli
 
@@ -66,7 +66,7 @@ func (f Fahrenheit) String() string {
 
 // KPascal is pressure at precision of 1Pa.
 //
-// Deprecated: This interface will be removed in v3. Use physic.KPascal
+// Deprecated: This interface will be removed in v3. Use physic.Pressure
 // instead.
 type KPascal Milli