Processing of `secondsSinceEpoch` and its reverse processing routine. (#80)

Merge pull request #77 from scivision/cmake

check return code and write message instead of crashing

use fpm directory layout

ci: consolidate

cmake: check compiler capabilities

Merge pull request #74 from wavebitscientific/increase-range-for-secondssinceepoch

Merge pull request #72 from scivision/docs

add a note and link to examples

minor style edits

remove unused variables

add test for secondsSinceEpoch of 100 years

use operator for clarity and more meaningful timedelta instance name

promote secondsSinceEpoch() to int64 so it can handle > 68 years; minor refactor for clarity

Merge pull request #73 from wavebitscientific/bump-version-to-1.7.1