feat(emacs/lean-input): shortcut for long arrow
fix(.travis.yml): trying to fix failure at travis
fix(frontends/lean): add 'eval' command
fix(util/sexpr/option_declarations): default value in help message, fixes #212
feat(library/unifier): add 'on-demand' choice constraints, they are processed as soon as their type does not contain meta-variables anymore
chore(frontends/lean/placeholder_elaborator): cleanup
refactor(*): use name_map
feat(frontends/lean): allow user to associate priorities to class-instances, closes #180
chore(frontends/lean/decl_cmds): disable incorrect warning message produced by gcc
feat(frontends/lean/elaborator): report an error when Type becomes a Prop after elaboration, closes #208
feat(frontends/lean/inductive_cmd): infer implicit argument annotation after elaboration, allow user to disable it by using '()' annotation, closes #210
fix(emacs/lean-syntax): use word-boundary instead of symbol-boundary
fix(emacs/lean-company): always allow typing for FIND_P
feat(emacs/lean-company): add auto-completion for option names
fix(frontends/lean/decl_cmds): warning message when compiling with clang++
feat(build): add 'CONSERVE_MEMORY' cmake option

When CONSERVE_MEMORY=ON and gcc is being used, we provide additional
command line options that will minimize the amount of memory used by gcc
when compiling Lean.
This is an attempt to fix the "out-of-memory" failures when building
Lean at Travis.
fix(emacs/lean-mode): trigger eri-indent only at the beginning of line
feat(frontends/lean): check modification time of imported files

Signed-off-by: Leonardo de Moura <leonardo@microsoft.com>
fix(emacs/lean-company): respect lean syntax to extract findp prefix

close #207
feat(kernel/expr): add hash_bi function that takes binder information into account