makefile: add lint target
lint: end each file with exactly one "\n"
lint: trim trailing whitespace
lint: convert each tab character to two spaces
lint: add missing semicolons
lint: replace leading commas with trailing commas
lint: fix inconsistent indentation
lint: make implicit blocks explicit
lint: remove unreferenced identifiers
lint: remove superfluous variable declarations
lint: add missing variable declarations
lint: replace double quotes with single quotes
lint: wrap long lines
lint: replace uses of == and != operators
lint: replace problematic "should" expressions
lint: use consistent spacing around operators
lint: replace uses of typeof and instanceof operators
lint: group and alphabetize imports
lint: remove unnecessary variable declarations
lint: remove noisy type annotations