Parsing: Allow both harmony and custom esprima versions.

Closes gh-560
Closes gh-680
Fixes #561
StringChecker: update docblock for constructor
Prepare for version 1.7.0
1.7.0
validateIndentation: fix empty multiline function body regression
Prepare for version 1.7.1
1.7.1
Cast StringChecker maxErrors property to Number the first time

In max-errors.js, Object.defineProperties cast the config maxErrors property to Number
but not the StringChecker maxErrors property.

This leads to a bug if multiple jscs checks are executed using the same config object
(config.maxerrors will equal 'undefined' the first time, and 'NaN' the second time)
StringChecker: unit test for when maxErrors is NaN

Closes gh-688
Closes gh-687
validateIndentation: fix return in switch failure

When a switch case only uses returns instead of breaks, treat the return indentation as the break indentation.

Closes gh-686
Fixes #684
Fix format of --esnext and --max-errors in README

These options were surrounded by single quotes instead of
backticks, so they were not formatted as code like the
other options.

Closes gh-683
CLI: fix order of options in help screen
Prepare for version 1.7.2
1.7.2
validateIndentation: handle breakless case stmts

Fixes #693
Parsing: Use the harmony parser via the esnext flag in the config

Closes gh-692
Fixes #691
Prepare for version 1.7.3
1.7.3
Readme: remove duplicative example for requireCurlyBraces
New rule: requireSpaceBeforeKeywords