Upgrade eslint; fix some new warnings and disable others

[cdhowie]

Upgrades eslint and related packages to the latest versions available. This fixes three of the bitHound dependency tests (#148). I will be preparing another PR to deal with the remaining five tests, but since this is a fairly far-reaching set of changes, I wanted this one to be reviewed separately.

New warnings either in eslint or in eslint-config-airbnb-base were subsequently triggered and resolved as follows:

• prefer-destructuring: Disabled. IMO, applying this rule is silly and results in intentionally-obtuse code.
• no-multi-assign: Disabled. There are many places where we publish functions on exports and internals simultaneously using chained assignments (a = b = c;). IMO, this is useful and makes the code clearer.
• prefer-spread: Disabled. The spread operator is not supported until Node 6, and we support back to Node 4 according to the CI build.
• object-curly-newline: Tweaked rule from airbnb-base to remove minParameters; resolved resulting warnings by reformatting object literals to either all be one one line or have one attribute per line.
• arrow-parens: Resolved warnings. (a => { } forms changed to (a) => { })
• function-paren-newline: Resolved warnings by reformatting some chained method calls to span multiple lines for improved clarity.
• import/newline-after-import: Resolved warnings by moving all non-require lines to follow require lines.
• no-buffer-constructor: Resolved warnings by changing the deprecated new Buffer(...) forms to Buffer.from(...).
• indent: Resolved warnings by applying consistent indentation rules to the few sections of code that did not conform.
• no-mixed-operators: Resolved warnings by using parens to explicitly group mathematical operations between different operators. (Particularly in forms like a - b * c, grouping like a - (b * c) makes the author's intent clear, even though that's what's happening anyway.)
• no-plusplus: Resolved warnings by changing all x++ forms to x += 1.
• space-unary-ops: Resolved warnings by changing typeof(x) forms to typeof x.
• no-prototype-builtins: Resolved warnings by replacing x.hasOwnProperty(y) forms with Object.prototype.hasOwnProperty.call(x, y).
• no-unused-vars: Resolved warnings by removing unused variable declarations.
• no-restricted-properties: Resolved warnings by replacing x.__defineGetter__() forms with equivalent Object.defineProperty() calls.
• no-useless-escape: Resolved warnings by removing unnecessary \ characters in string literals.

[cdhowie]

@clarkie @dangerginger If you guys are able to review this, I would like to get it done sooner rather than later; it touches nearly every source file and there is a high change it will conflict with any future merged PRs.

[coveralls]

Coverage decreased (-0.08%) to 98.541% when pulling f1b343a on cdhowie:update-dependencies into a14b760 on clarkie:master.

[cdhowie]

@clarkie @dangerginger Since there's been no review activity in 15+ days, I just pushed this. I don't want to hold this up.