add NumericSpec.exponentChar

Author: 9il

source/mir/bignum/decimal.d

@@ -408,7 +408,7 @@ struct Decimal(size_t maxSize64)
 
  // prints e+/-exponent
  auto expLength = printSignedToTail(exponent, buffer0[$ - N - 16 .. $ - 16], '+');
- buffer[$ - ++expLength] = 'e';
+ buffer[$ - ++expLength] = spec.exponentChar;
  w.put(buffer[$ - expLength .. $]);
  }
 

source/mir/format.d

@@ -208,6 +208,9 @@ struct NumericSpec
  ///
  Format format;
 
+ /// Defaults to 'e'
+ char exponentChar = 'e';
+
  /++
  Precise output with explicit exponent.
  Examples: `1e-6`, `6e6`, `1.23456789e-100`.