Add parse bin int, fixes #8018 (#8020)

* clarify `parseHexInt`, `parseOctInt` docstring and exception msgs

* add `parseBinInt` based on `parseutil.parseBin` implementation

Adds a `parseBinInt`, which parses a binary integer string and returns
it as an integer. This is based on the implementation of
`parseutil.parseBin`, removing the unnecessary parts.

* add tests for all `parse(Hex|Oct|Bin)Int` procs

* replace `parse*Int` proc impls by call to parseutil procs

Replaces the `parse(Hex|Oct|Bin)Int` procedure implementation by calls
to the `parseutil` procs, which receive a mutable argument.

Has the main advantage that the empty string as well as a "prefix
only" string, e.g. "0x" counts as an invalid integer.

Also moves the `parseOctInt` proc further up in the file so that all
`parse` procs are below one another.

* replace `var L` by `let L` in `parse` procs

There's no reason for the usage of `var` here.

* add `maxLen` optional arg for `parseutil.parse(Oct|Bin)`

Plus small change to test cases.

* update changelog about `parse*Int` procs

* fix `rejectParse` template in `tstrutils`

* make sure only `s.len` chars are parsed, if `maxLen+start` > s.len

Fixes a previous bug in `parseHex` (and now affected `parseOct` and
`parseBin`), which allowed to set `start + maxLen` to be larger than
the strings length. This resulted in an out of bounds access.

* move `parse*Int` proc change to breaking changes, add double `

tests/stdlib/tstrutil.nim

@@ -7,6 +7,14 @@ discard """
 import
   strutils
 
+import macros
+
+template rejectParse(e) =
+  try:
+    discard e
+    raise newException(AssertionError, "This was supposed to fail: $#!" % astToStr(e))
+  except ValueError: discard
+
 proc testStrip() =
   write(stdout, strip("  ha  "))
 
@@ -148,7 +156,6 @@ proc testDelete =
   delete(s, 0, 0)
   assert s == "1236789ABCDEFG"
 
-
 proc testIsAlphaNumeric =
   assert isAlphaNumeric("abcdABC1234") == true
   assert isAlphaNumeric("a") == true
@@ -203,10 +210,50 @@ proc testCountLines =
   assertCountLines("\nabc\n123")
   assertCountLines("\nabc\n123\n")
 
+proc testParseInts =
+  # binary
+  assert "0b1111".parseBinInt == 15
+  assert "0B1111".parseBinInt == 15
+  assert "1111".parseBinInt == 15
+  assert "1110".parseBinInt == 14
+  assert "1_1_1_1".parseBinInt == 15
+  assert "0b1_1_1_1".parseBinInt == 15
+  rejectParse "".parseBinInt
+  rejectParse "_".parseBinInt
+  rejectParse "0b".parseBinInt
+  rejectParse "0b1234".parseBinInt
+  # hex
+  assert "0x72".parseHexInt == 114
+  assert "0X72".parseHexInt == 114
+  assert "#72".parseHexInt == 114
+  assert "72".parseHexInt == 114
+  assert "FF".parseHexInt == 255
+  assert "ff".parseHexInt == 255
+  assert "fF".parseHexInt == 255  
+  assert "0x7_2".parseHexInt == 114
+  rejectParse "".parseHexInt
+  rejectParse "_".parseHexInt
+  rejectParse "0x".parseHexInt
+  rejectParse "0xFFG".parseHexInt
+  rejectParse "reject".parseHexInt
+  # octal
+  assert "0o17".parseOctInt == 15
+  assert "0O17".parseOctInt == 15
+  assert "17".parseOctInt == 15
+  assert "10".parseOctInt == 8
+  assert "0o1_0_0".parseOctInt == 64
+  rejectParse "".parseOctInt
+  rejectParse "_".parseOctInt
+  rejectParse "0o".parseOctInt
+  rejectParse "9".parseOctInt
+  rejectParse "0o9".parseOctInt
+  rejectParse "reject".parseOctInt
+
 testDelete()
 testFind()
 testRFind()
 testCountLines()
+testParseInts()
 
 assert(insertSep($1000_000) == "1_000_000")
 assert(insertSep($232) == "232")