Normally an alignment method would round values down to the alignment boundary. The current mem.align functionality, however, rounds values up - which is a bit unexpected. This PR changes mem.align to round values down as one would expect, and adds a new method mem.round_up to retain the old functionality in a more intuitive way.

Changes:

• Rename mem.align to mem.align_up
• Implement a new mem.align method
• Accomodate usages to the new functionlity
• Use mem.align and mem.align_up where appropriate (code de-duplication)