Add first kernel construction and its support

Add first kernel construction and its support

The supporting changes consist of changing the ft_token_dup function to
take pointer to token as input. Taking global static token caused some
error but was solved by passing pointer.
Function to free structs now handle NULL gracefully. This was
encountered because not all used structures are initialized yet.

The zeroth rule is added to generate a table, that returns the original
first token as a root of the table. The type of NULL cannot be achieved
any other way inside the table.rules.