Use latest FreeBSD when running unit tests in sr.ht
octaspire_string_t: add two functions and unit tests

* Add functions for checking if 'octaspire_string_t'
  starts or ends with the given C string.
Update GNUmakefile and README.md, git tag versions
Fix one more unit test case for MSVC
Try to fix some of the unit tests for MSVC
Fix Windows MinGW build, update documentation

* The commit adding Windows MSVC (Visual Studio C/C++)
  support broke the Windows MinGW build. This commit
  should hopefully fix it without breaking the Windows
  MSVC build.

* Update the Core manual by adding instructions for
  building with Visual Studio C/C++ in Windows.
Fix WIN32 build

* Fix a typo from previous commit
Add support for MSVC C/C++ compiler

* Tested with 'Visual Studio 2017 (Community edition)'

  Usage:

  0. Download and install required tools from the
     internet:

     * 'Visual Studio 2017 (Community edition)'
     * 'git'

  1. Start 'Developer Command Prompt for VS 2017'.
     It can be found under 'Visual Studio 2017' in
     the start menu.

     Please note, that you cannot use regular windows
     command prompt.

  2. Change to a directory you want to use. For example:

     cd c:\

  3. Clone the development repository using git:

     git clone https://github.com/octaspire/core.git

  4. Change into the correct directory for using 'Core':

     cd core\release

  5. Build unit test runner and an example program with command:

     how-to-build\windows-msvc.bat

     You should now have two executable programs
     (unit test runner and an example program) and
     also instructions for building those programs.

     Please note, that the recommended way of using
     Core is to use the amalgamation. It is just
     one source file that contains _everything_.

     So hopefully there should be no need for any
     build tool (like make, gmake, nmake or ninja)
     or metabuild tool (like CMake).
Fix for Dern in Plan9, update GNUmakefile
Remove submodule
Fix for Dern Plan9 build
Add helper function for creating string vectors
Use faster Wagner-Fischer algorithm to calculate Levenshtein distance
Fix codestyle
Add recursive Levenshtein distance for strings, fix compiler warnings

* Add slow recursive Levenshtein distance implementation for
  strings. It should be replaced with a more efficient
  iterative algorithm later.

* Fix compiler warnings.

* Fix amalgamation script.

* Add two build manifests for builds.sr.ht.
Change the way the manual is generated
Add version number accessors into SemVer
Add new functions and unit tests for SemVer
Continue SemVer implementation, fix memory leaks in vector container
Modify semantic versioning implementation, add few unit tests
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