v2.4

Public release of the MvsSln 2.4

* FIXED: "The format ... of configuration is not supported". Issue #19.

* FIXED: Fixed loading of projects via `IsolatedEnv.LoadProjects()`.

* FIXED: Fixed possible NullReferenceException in `ProjectItem` constructors.

* NEW: Introduces XProjectEnv. PR #17.
       An splitted IsolatedEnv as the base but without IDisposable.
    ```
    IXProjectEnv slnEnv;
    ...
    slnEnv = new XProjectEnv(sln, properties);
    ...
    slnEnv = new IsolatedEnv(sln); // +IEnvironment, +IDisposable
    slnEnv.Assign();
    ...
    ((IDisposable)slnEnv)?.Dispose();
    ```

* NEW: Added `PropertyNames` type. Regular MSBuild Properties and related.

* NEW: Added `FileExt` type for work with `ProjectType` via its file only.

* NEW: Added `Kinds` type: PRJ_UNLOADED; PRJ_SLN_DIR

* NEW: New extension methods:
    ```
    +TVal GetOrDefault<TKey, TVal>(this IDictionary<TKey, TVal> data, TKey key, TVal def)
    +bool IsEqual(this Project a, Project b)
    +string GetSolutionDir(this Project eProject)
    +string GetProjectRelativePath(this Project eProject)
    +string GetConfig(this Project eProject)
    +string GetPlatform(this Project eProject)
    +string GetSolutionExt(this Project eProject)
    string GetDirectoryFromFile(this string file)
    Dictionary<string, string> GetFileProperties(this string file)
    IDictionary<string, string> AddOrUpdate(this IDictionary<string, string> source, IDictionary<string, string> items)
    bool Remove<T>(this IList<T> src, T elem, Func<T, T, bool> comparer)
    bool IsLimEqual(this IXProject x, IXProject prj)
    ```

* CHANGED: Removed pGuid checking from `IXProjectEnv.GetOrLoadProject()`
           Related to Issue #18.

* CHANGED: ISlnResult changes:
    ```
    +`string SolutionFile`
        Full path to an solution file.
        Old versions still can address it through Properties.
    ```

* CHANGED: IConfPlatform changes:
    ```
    +`bool IsEqualByRule(string config, string platform, bool icase = false);`
        Checking an config/platform by using {Rule} instance.
    ```

* CHANGED: IXProjectEnv (IEnvironment) changes:
    ```
    +`IXProject XProjectByFile(...);`
        Find project by full path to file.

    +`IEnumerable<IXProject> Assign(IEnumerable<Project> projects = null);`
        Assign an existing `Microsoft.Build.Evaluation.Project` instances for local collection.

    +`IXProject AddOrGet(Project project);`
        Adds `Microsoft.Build.Evaluation.Project` instance into IXProject collection if it does not exist.

    +`ProjectItemCfg ExtractItemCfg(Project project);`
        Prepares data from `Microsoft.Build.Evaluation.Project` instance.

    +`void UnloadAll(bool throwIfErr = true);`
        Unloads all evaluated projects at current time.

    +`bool Unload(IXProject xp);`
        Unloads specified project.

    +`IEnumerable<Project> ValidProjects`
        List of valid projects such as something except `.user`,`.metaproj` but contains FirstChild / LastChild XML node.
    ```

* CHANGED: Updated package's tool hMSBuild 2.2

           Release notes:
           https://github.com/3F/hMSBuild/releases/tag/v2.2

* NOTE: The most 2.4 changes is relevant to integration with vsSolutionBuildEvent.

        https://twitter.com/GitHub3F/status/1158091930309398528
        https://github.com/3F/vsSolutionBuildEvent/pull/53
        https://github.com/3F/MvsSln/pull/17

        Find any relevant use of the new features in that project.