SchemaShell always uses --file param when present.

Addresses **part** of the problem described in #4174.

Corrects SchemaShell's startup logic so that when a `--file` param is provided by the user, it is always used even in the case that it matches the default file name (schema.php). This solves a problem when a user wishes to provide a classname using `--name`, but still wants to use the default filename.
More predictable default for CakeShema class naming.

Instead of using the `APP_DIR` constant, which may change between developer installations of a project and cause issues loading Schemas generated elsewhere, use a fixed string, 'App'.

This is related to CakeDC/migrations#184 and should fully resolve #4174.
Figures it'd be a missing paren.
Corrects logic to only apply default filename in **all** cases where none provided.
CakeSchema naming fallback.

Abstracts the `require_once` of the schema file so it can be done twice. The added second call is a fallback for the previous APP_DIR-based naming to provide backwards compatibility.

Removes now-obsolete CakeSchema tests that involved `Configure::read('App.dir')`. The CakeSchema::name is now always static (and predictable) in the default case.
Code sniff fix.
Doc block capitalization corrections as requested.
Merge pull request #4230 from beporter/bug/schemashell-name-file-params-fix

SchemaShell --name and --file params priority fix.

Fixes #4174
Adds a link to the README for people like me that don't spot the CONTRIBUTING.md file in root folder.
Added additional 3.0 doc link.
Style tweak.
All CakeSchema doc blocks conform to coding standards.

As laid out here: http://book.cakephp.org/2.0/en/contributing/cakephp-coding-conventions.html#typehinting
Merge pull request #4245 from beporter/cakeschema-style-guide-updates

Improve docblock formatting.
Merge pull request #4244 from beporter/add-contributing-pointer-to-readme

Add "contributing" pointers to GitHub readme