Add "DIVIDE" command and new "maxslope" and "maxslopecost" parameters (#642)

* Added 'DIV' expression for profiles

* Added 'uphillmaxbuffercost' and 'downhillmaxbuffercost' parameter. This makes it possible to penalize very steep path sections

* Added 'div by zero' check in BExpression.java DIV command

* Simplify maxbuffercostdiv logic

* Added documentation about new features

* Fix typo

* Rename new DIV command

* Redesign the new commands
- Allow to set both the maxslope and the maxslopecost in the way context separately for uphill and downhill
- New names for the new commands that better reflect what they actually do

* Adapt the profile developers guide to the latest changes

* Improve wording

---------

Co-authored-by: quaelnix <122357328+quaelnix@users.noreply.github.com>

docs/developers/profile_developers_guide.md

@@ -72,12 +72,16 @@ Some variable names are pre-defined and accessed by the routing engine:
 
 - for the global section these are:
 
-  - 7 elevation configuration parameters:
+  - 11 elevation configuration parameters:
 
     - `downhillcost`
     - `downhillcutoff`
+    - `downhillmaxslope`
+    - `downhillmaxslopecost`
     - `uphillcost`
     - `uphillcutoff`
+    - `uphillmaxslope`
+    - `uphillmaxslopecost`
     - `elevationpenaltybuffer`
     - `elevationmaxbuffer`
     - `elevationbufferreduce`
@@ -172,6 +176,7 @@ All expressions have one of the following basic forms:
   - `and      <boolean expression 1> <boolean expression 2>`
   - `xor      <boolean expression 1> <boolean expression 2>`
   - `multiply <numeric expression 1> <numeric expression 2>`
+  - `div      <numeric expression 1> <numeric expression 2>`
   - `add      <numeric expression 1> <numeric expression 2>`
   - `sub      <numeric expression 1> <numeric expression 2>`
   - `max      <numeric expression 1> <numeric expression 2>`
@@ -276,33 +281,37 @@ it climbed only 10 m on those 500 m, all 10 m would be *swallowed* by cutoff,
 together with up to 5 m from the buffer, if there were any.
 
 When elevation does not fit the buffer of size `elevationmaxbuffer`, it is
-converted by up/downhillcost ratio to Elevationcost portion of Equivalentlength.
-Up/downhillcostfactors are used, if defined, otherwise costfactor is used.
+converted by `up/downhill[maxslope]cost` ratio to Elevationcost portion of Equivalentlength.
+`up/downhillcostfactors` are used, if defined, otherwise `costfactor` is used.
 
 - `elevationpenaltybuffer` - default 5(m).
 
   The variable value is used for 2 purposes
 
   - with `buffer content > elevationpenaltybuffer`, it starts partially convert
-    the buffered elevation to ElevationCost by Up/downhillcost
+    the buffered elevation to ElevationCost by `up/downhillcost`
 
   - with `elevation taken = MIN (buffer content - elevationpenaltybuffer, WayLength[km] * elevationbufferreduce*10`
-    Up/downhillcost factor takes place instead of costfactor at the percentage
+    The `up/downhillcostfactor` takes place instead of `costfactor` at the percentage
     of how much is `WayLength[km] * elevationbufferreduce*10` is saturated by
     the buffer content above elevationpenaltybuffer.
 
 - `elevationmaxbuffer` - default 10(m)
 
   is the size of the buffer, above which all elevation is converted to
-  Elevationcost by Up/Downhillcost ratio, and - if defined -
-  Up/downhillcostfactor fully replaces costfactor in way cost calculation.
+  Elevationcost by `up/downhill[maxslope]cost` ratio, and - if defined -
+  `up/downhillcostfactor` fully replaces `costfactor` in way cost calculation.
 
 - `elevationbufferreduce` - default 0(slope%)
 
   is rate of conversion of the buffer content above elevationpenaltybuffer to
   ElevationCost. For a way of length L, the amount of converted elevation is
   L[km] * elevationbufferreduce[%] * 10. The elevation to Elevationcost
-  conversion ratio is given by Up/downhillcost.
+  conversion ratio is given by `up/downhill[maxslope]cost`.
+
+Whether `up/downhillmaxslope` or `up/downhillmaxslopecost` is used as conversion
+ratio depends on whether the elevation was accumulated below or above the slope
+threshold values defined in `up/downhillmaxslope`.
 
 Example:   Let's examine steady slopes with `elevationmaxbuffer=10`,
 `elevationpenaltybuffer=5`, `elevationbufferreduce=0.5`, `cutoffs=1.5`,
@@ -313,7 +322,7 @@ All slopes within 0 .. 1.5% are swallowed by the cutoff.
 - For slope 1.75%, there will remain 0.25%.
 
   That saturates the elevationbufferreduce 0.5% by 50%. That gives Way cost to
-  be calculated 50% from costfactor and 50% from Up/downhillcostfactor.
+  be calculated 50% from `costfactor` and 50% from `up/downhillcostfactor`.
   Additionally, 0.25% gives 2.5m per 1km, converted to 2.5*60 = 150m of
   Elevationcost.