to MeasureUnit *

  - added wrappers for MeasureUnit.product(), reciprocal(), getDimensionality()
  - added wrapper for MeasureUnit.forIdentifier()

* Add installation instructions to README.md

* Update instructions concerning C-compilers

* Link to C-compiler explanation

* Link to packages.debian.org/source/stable/pyicu

* Fix typo

  - added wrappers for DateIntervalFormat.get/setContext()
  - added wrapper for LocaleMatcher.isMatch()
  - added wrapper for LocaleMatcherBuilder.setDirection()
  - added wrappers LocaleMatcherBuilder.setMaxDistance(), setNoDefaultLocale()
  - added wrappers for MeasureUnit.getComplexity() and UMeasureUnitComplexity
  - added wrapper for MeasureUnit.getIdentifier()
  - switched MeasureUnit.__str__() to use MeasureUnit::getIdentifier()  
  - added wrappers for new MeasureUnit static factory methods
  - added wrapper for FormattedNumber.getOutputUnit()
  - added wrapper for FormattedNumberRange.getDecimalNumbers()
  - added wrappers for PluralRules.select(FormattedNumber|Range)

 - fixed parameter order inversion in parsing args to UBidiTransform.transform

  - added support for python 3.9 in CI

Adapted passing version flags on win32 syntax to reflect Python 3.9 changes.
Fixed memory leaks in error situations in Bidi wrappers.

`PyUnicode_FromStringAndSize(NULL, size)` usage is also deprecated.

* Update break.py to python 3

* Update strsrch.py to python 3

  - reworked BY_VALUE type wrappers to have "&&" overload

  - made FormattedValue iterable via nextPosition()
  - added wrappers for FormattedDateInterval, FormattedNumber, FormattedList
  - added wrappers for FormattedRelativeDateTime and enums
  - added wrappers for UNumberFormatFields, UNumberFormatAttribute
  - added wrappers for NumberRangeFormatter, FormattedNumberRange and enums