💥✏️Change liter abbreviations to lowercase l (v6) (#1404)

Fixes #1115

Change from `L` to `l` in unit abbreviations for liters, to be
consistent in library and to follow SI Unit System conventions.

Note:
- Parsing is backwards compatible, since parsing unit abbreviations has
fallback to case insensitive as long as there is no ambiguity. E.g.
`Volume.Parse("10 L")` and `Volume.Parse("10 l")` both work.
- To avoid breaking backwards compatibility, we keep `liter` instead of
`litre` when naming units.

Also updated wiki:

https://github.com/angularsen/UnitsNet/wiki/Adding-a-New-Unit#abbreviation-naming-conventions

### Changed units
- `Density.GramPerLiter` + prefixes
- `FuelEfficiency.LiterPer100Kilometers`
- `FuelEfficiency.KilometerPerLiter`
- `MassConcentration.GramPerMicroliter`
- `MassConcentration.GramPerMilliliter`
- `MassConcentration.GramPerDeciliter`
- `MassConcentration.GramPerLiter`
- `Molarity.MolePerLiter`
- `VolumeConcentration.LitersPerLiter`
- `VolumeConcentration.LitersPerMililiter`
- `VolumeFlow.LiterPerSecond`
- `VolumeFlow.LiterPerMinute`
- `VolumeFlow.LiterPerHour`
- `VolumeFlow.LiterPerDay`

Author: angularsen

Common/UnitDefinitions/Density.json

@@ -191,7 +191,7 @@
       "Localization": [
         {
           "Culture": "en-US",
-          "Abbreviations": [ "g/L" ]
+          "Abbreviations": [ "g/l" ]
         }
       ]
     },

Common/UnitDefinitions/FuelEfficiency.json

@@ -11,7 +11,7 @@
         "Localization": [{
           "Culture": "en-US",
           "Abbreviations": [
-            "L/100km"
+            "l/100km"
           ]
         }]
       },
@@ -47,7 +47,7 @@
         "Localization": [{
           "Culture": "en-US",
           "Abbreviations": [
-            "km/L"
+            "km/l"
           ]
         }]
       }

Common/UnitDefinitions/MassConcentration.json

@@ -76,7 +76,7 @@
       "Localization": [
         {
           "Culture": "en-US",
-          "Abbreviations": [ "g/μL" ]
+          "Abbreviations": [ "g/μl" ]
         }
       ]
     },
@@ -93,7 +93,7 @@
       "Localization": [
         {
           "Culture": "en-US",
-          "Abbreviations": [ "g/mL" ]
+          "Abbreviations": [ "g/ml" ]
         }
       ]
     },
@@ -106,7 +106,7 @@
       "Localization": [
         {
           "Culture": "en-US",
-          "Abbreviations": [ "g/dL" ]
+          "Abbreviations": [ "g/dl" ]
         }
       ]
     },
@@ -123,7 +123,7 @@
       "Localization": [
         {
           "Culture": "en-US",
-          "Abbreviations": [ "g/L"]
+          "Abbreviations": [ "g/l"]
         }
       ]
     },

Common/UnitDefinitions/Molarity.json

@@ -38,7 +38,7 @@
       "Localization": [
         {
           "Culture": "en-US",
-          "Abbreviations": [ "mol/L", "M" ]
+          "Abbreviations": [ "mol/l", "M" ]
         }
       ]
     },

Common/UnitDefinitions/VolumeConcentration.json

@@ -25,7 +25,7 @@
       "Localization": [
         {
           "Culture": "en-US",
-          "Abbreviations": [ "L/L" ]
+          "Abbreviations": [ "l/l" ]
         }
       ]
     },
@@ -38,7 +38,7 @@
       "Localization": [
         {
           "Culture": "en-US",
-          "Abbreviations": [ "L/mL" ]
+          "Abbreviations": [ "l/ml" ]
         }
       ]
     },

Common/UnitDefinitions/VolumeFlow.json

@@ -185,7 +185,7 @@
       "Localization": [
         {
           "Culture": "en-US",
-          "Abbreviations": [ "L/s", "LPS" ]
+          "Abbreviations": [ "l/s", "LPS" ]
         },
         {
           "Culture": "ru-RU",
@@ -202,7 +202,7 @@
       "Localization": [
         {
           "Culture": "en-US",
-          "Abbreviations": [ "L/min", "LPM" ]
+          "Abbreviations": [ "l/min", "LPM" ]
         },
         {
           "Culture": "ru-RU",
@@ -219,7 +219,7 @@
       "Localization": [
         {
           "Culture": "en-US",
-          "Abbreviations": [ "L/h", "LPH" ]
+          "Abbreviations": [ "l/h", "LPH" ]
         },
         {
           "Culture": "ru-RU",
@@ -236,7 +236,7 @@
       "Localization": [
         {
           "Culture": "en-US",
-          "Abbreviations": [ "l/day", "L/d", "LPD" ]
+          "Abbreviations": [ "l/day", "l/d", "LPD" ]
         }
       ]
     },