src: improved some codes
src: improved readability
src: added 'detail/is_eigen_block.hpp'
src: added 'Block'
src: supported 'Block'
src: added 'Block'
readme: deleted 'Getting Started' and added 'Installation'
src: fixed a mistake
src: added instance method 'Block.toString()'
src: improved some codes
src: added a constructor for Block
src: added Block type
src: added instance method 'Matrix.block()'
readme: updated for some mistakes
src: rename 'Block' and CBlock' to 'MatrixBlock' and 'CMatrixBlock'
src: added 'detail::unwrap_eigen_block.hpp'
src: rename 'detail::unwrap_block' to 'detail::unwrap_eigen_block'
src: remove redundant code
makefile: improve readability
src: adstract instance methods 'rows()' and 'cols()'