Fix typo in transactions.c
Add declaration and stub of transaction runner function
Add missing inclusion I somehow managed to remove

..while squashing, I guess.
Add code for stack preparation
Add code for initialisation of the processor
Add code for executing the transaction
Add code for constructing the value return message
Add preliminary version of function processing transactions
Merge pull request #247 from neithernut/add-transaction_processing_function

Add transaction processing function