Fix linting and Makefile issues (#2)

* Add single-offset-storage method for performance

In promisified mode, offsets are stored after every single message
Calling into FFI is already not cheap and on top of that, the
offsetsStore method does a lot of allocations because it needs to make a
vector etc. etc. This method change yields a benefit of 8%.

Also reduces dynamic casts by storing a reference to the rdkafka
consumer.

* Remove jshint and expand eslint coverage

Many changes within, but only cosmetic:
1. remove jshint as it's rather unmaintained and we don't need 2
   linters.
2. update eslint to latest possible version.
3. update eslint coverage to include old API and promisified tests.
4. update makefile accordingly
5. fix lint errors.

* Update Makefule, update cpplint to latest version

* Comply with cpplint

Author: milindl

.eslintrc.js

@@ -1,15 +1,9 @@
 NODE-GYP ?= node_modules/.bin/node-gyp
 
-# Sick of changing this. Do a check and try to use python 2 if it doesn't work
-PYTHON_VERSION_FULL := $(wordlist 2,4,$(subst ., ,$(shell python --version 2>&1)))
-PYTHON_VERSION_MAJOR := $(word 1,${PYTHON_VERSION_FULL})
-
-ifeq ($(PYTHON_VERSION_MAJOR), 2)
 PYTHON = python
-else
-PYTHON = python2
+ifeq (, $(shell command -v python))
+  PYTHON = python3
 endif
-
 NODE ?= node
 CPPLINT ?= cpplint.py
 BUILDTYPE ?= Release
@@ -24,9 +18,7 @@ CONFIG_OUTPUTS = \
   build/binding.Makefile build/config.gypi
 
 CPPLINT_FILES = $(wildcard src/*.cc src/*.h)
-CPPLINT_FILTER = -legal/copyright
-JSLINT_FILES = lib/*.js test/*.js e2e/*.js lib/kafkajs/*.js
-ESLINT_FILES = lib/kafkajs/*.js test/promisified/*.js
+CPPLINT_FILTER = -legal/copyright,-readability/todo,-whitespace/indent_namespace,-runtime/references
 
 PACKAGE = $(shell node -pe 'require("./package.json").name.split("/")[1]')
 VERSION = $(shell node -pe 'require("./package.json").version')
@@ -40,16 +32,13 @@ endif
 
 all: lint lib test e2e
 
-lint: cpplint jslint eslint
+lint: cpplint eslint
 
 cpplint:
 	@$(PYTHON) $(CPPLINT) --filter=$(CPPLINT_FILTER) $(CPPLINT_FILES)
 
-jslint: node_modules/.dirstamp
-	@./node_modules/.bin/jshint --verbose $(JSLINT_FILES)
-
 eslint: node_modules/.dirstamp
-	@./node_modules/.bin/eslint $(ESLINT_FILES)
+	@./node_modules/.bin/eslint .
 
 lib: node_modules/.dirstamp $(CONFIG_OUTPUTS)
 	@PYTHONHTTPSVERIFY=0 $(NODE-GYP) build $(GYPBUILDARGS)