Fix various details in README.md (#335)

Add newline after heading and code block (consistency).

Use triple backticks for bash code examples.

Change how library will be installed via composer.

Remove explicit version constraint in `composer require` example. Recent
versions of composer will default the most recent version and
set a non-major breaking constraint.
Version constraint was still pointing to the most recent version of 2.*
release.

Soft limit text to 80 chars (does node affect code examples).

Remove 'Basic usage' heading.

Fix heading 'Type coercion' (space and typo).

Add missing opening PHP tag (section 'Type coercion'.

Fix indentation in code example (consistent 4 spaces).

Use single backticks for inline code.
Add parenthesis to method in description.

Author: rtucek

README.md

@@ -12,19 +12,20 @@ See [json-schema](http://json-schema.org/) for more details.
 
 ### Library
 
-    $ git clone https://github.com/justinrainbow/json-schema.git
+```bash
+git clone https://github.com/justinrainbow/json-schema.git
+```
 
-### Dependencies
+### Composer
 
-#### [`Composer`](https://github.com/composer/composer) (*will use the Composer ClassLoader*)
+[Install PHP Composer](https://getcomposer.org/doc/00-intro.md)
 
-    $ wget http://getcomposer.org/composer.phar
-    $ php composer.phar require justinrainbow/json-schema:~2.0
+```bash
+composer require justinrainbow/json-schema
+```
 
 ## Usage
 
-### Basic usage
-
 ```php
 <?php
 
@@ -43,17 +44,23 @@ if ($validator->isValid()) {
     }
 }
 ```
-###Type Coercion
-If you're validating data passed to your application via HTTP, you can cast strings and booleans to the expected types defined by your schema:
+
+### Type coercion
+
+If you're validating data passed to your application via HTTP, you can cast strings and booleans to
+the expected types defined by your schema:
+
 ```php
+<?php
+
 use JsonSchema\SchemaStorage;
 use JsonSchema\Validator;
 use JsonSchema\Constraints\Factory;
 use JsonSchema\Constraints\Constraint;
 
 $request = (object)[
-   'processRefund'=>"true",
-   'refundAmount'=>"17"
+    'processRefund'=>"true",
+    'refundAmount'=>"17"
 ];
 
 $factory = new Factory( null, null, Constraint::CHECK_MODE_TYPE_CAST | Constraint::CHECK_MODE_COERCE );
@@ -75,7 +82,7 @@ is_bool($request->processRefund); // true
 is_int($request->refundAmount); // true
 ```
 
-Note that the ```CHECK_MODE_COERCE``` flag will only take effect when an object is passed into the ```check``` method.
+Note that the `CHECK_MODE_COERCE` flag will only take effect when an object is passed into the `check()` method.
 
 ### With inline references
 
@@ -133,4 +140,6 @@ $jsonValidator->check($jsonToValidateObject, $jsonSchemaObject);
 
 ## Running the tests
 
-    $ vendor/bin/phpunit
+```bash
+vendor/bin/phpunit
+```