Remove solution folders

// test.sln with 3 projects, proj1.csproj, solFldr, solFldr/proj2.csproj 
var solution = ParseSolution(new FilePath("test.sln"));

// returns proj1.csproj, proj2.csproj
solution.GetProjects(); 

// returns proj1.csproj, solFldr, solFldr/proj2.csproj
solution.Projects;

Identifies a SolutionProject as a solution folder type

// test.sln { proj1.csproj, solutionFolder }
var projects = ParseSolution(new FilePath("test.sln")).Projects;

projects[0].IsSolutionFolder(); // false
projects[1].IsSolutionFolder(); // true

Identifies a SolutionProject by type

// test.sln { proj1.csproj, solutionFolder }
var projects = ParseSolution(new FilePath("test.sln")).Projects;

projects[0].IsType(ProjectTypes.CSharp); // true
projects[1].IsType(ProjectTypes.SolutionFolder); // true