Rename 0_Introduction.markdown to 0_Introduction.md
Rename 1_Installation.markdown to 1_Installation.md
Rename 2_Usage_of_basic_components.markdown to 2_Usage_of_basic_components.md
Rename 3_Other_node_tree_representations.markdown to 3_Other_node_tree_representations.md
Rename 4_Code_generation.markdown to 4_Code_generation.md
Rename Lexer.markdown to Lexer.md
Merge pull request #1 from anezi/rename_markdown_files

Rename markdown files