Added reason and cost arguments to transaction methods

• Transaction methods that modify the stock in some way now offer an optional $reason and $cost parameter to correctly update the stock record when a stock event takes place.
• Added more documentation and tests to match

Refactored InventoryTransactionTrait

• Refactored InventoryTransactionTrait, minimizing its previous large size

Fixed static boot methods

• Boot methods in traits have been renamed to boot(Trait Name) to use eloquent's trait auto-booting
• Added more localization fields in preparation for transactions update
• Small test update

Merged pulls

• Merged 5c8c7e5
• Merged 0dc54eb

Added new SKU functions

• Added 2 (two) new SKU functions on inventory items (createSku($code, $overwrite = false) & updateSku($code, $sku = NULL)
• Calling newStockOnLocation($location) now throws an exception if a stock already exists on the specified location
• Updated documentation and tests to match

Added new inventory method, updated docs

• Added Inventory method $item->newStockOnLocation($location)
• Updated documentation in code and readme's

Inventory Transactions

• Added Inventory Transactions
• Revamped documentation

Added missing use Lang statement in supplier trait

Added missing use Illuminate\Support\Facades\Lang; statement in supplier trait

Small code formatting changes

• Inventory::findBySku() now does not open a new query builder instance to check for the existence of the item
• Code formatting tweaks

Fixed caching issue, updated tests

• Fixed caching issue
• Regenerating an sku (via $item->regenerateSku() now generates an SKU if one doesn't exist
• Updated tests