chore(library/Makefile): remove unused Makefile
feat(emacs/lean-type): add lean-show-type-add-to-kill-ring option

If a customization option 'lean-show-type-add-to-kill-ring' is non-nil
and a user runs 'lean-show-type' by explicitly typing 'C-c C-t',
lean-mode saves the displayed type information message into kill-ring
, which can be pasted by yank (C-y) command.

Close #245
fix(library/module): race condition on m_imported
fix(kernel/constraint): bug in operator<<
feat(kernel/converter): relax is_def_eq test for local constants and meta-variables
chore(library/simplifier): delete old simplifier

This was the simplifier used in Lean 0.1.
chore(library/rewriter): remove lean-0.1 files
refactor(library/tactic): elaborate expressions nested in tactics with respect to current goal, save postponed constraints (e.g., flex-flex constraints) closes #44, fixes #70
feat(library/tactic/proof_state): apply substitutions when pretty printing state
fix(frontends/lean/elaborator): perform translation using "user-level" names
feat(library/tactic): add 'rename' hypothesis tactic
feat(bin/linja): add --discard and --to_axiom options
feat(util/lean_path.cpp): use '/library' as LEAN_PATH for emscripten
feat(shell/lean.cpp): expose functions to javascript side

lean_init, lean_import_module, lean_process_file
feat(CMakeLists.txt): support emscripten
fix(emacs/lean-util): fix lean-path-list to only include existing dirs

Fix #246
fix(style): remove "using namespace emscripten"
refactor(library): move flycheck "helper" classes to separate module
refactor(library/tactic/apply_tactic): remove dead code
refactor(library/tactic/apply_tactic): reuse type_checker object