issue#8 added Day Type from time library

[AR2202]

I added the 'Day' type from the time library, which represents a Date. This is a first attempt and if this is OK, I can add more types from the time library.

[ocramz]

Thank you! Looks good.

As you might have noticed there are two overlapping pieces of API: the 'getX' functions and the Traversal s. I like traversals better as they are more flexible but this is a longer-term design question, to be explored with concrete examples.

[AR2202]

I've added some additional types now.

[AR2202]

Sorry, I've noticed that the checks in the CI failed, but I don't know why that is. It builds and tests pass locally on my machine.

[ocramz]

@AR2202 the CI error is due to the version bound on the hashable-time dependency, see below.
This is due to the fact that we run CI against different Stackage snapshots, which reference various versions of packages.
One way forward would be to relax the lower bound on hashable-time, provided the needed functionality exists in previous versions.
On the other hand, I see that hashable-time has been superseded by time-compat https://hackage.haskell.org/package/time-compat , because Haskellers do be like that sometimes.

Error: While constructing the build plan, the following exceptions were encountered:

In the dependencies for heidi-0.3.1:

hashable-time-0.2.0.2 from stack configuration does not match >=0.2.1 

                      (latest matching version is 0.3)

needed since heidi is a build target.

Some different approaches to resolving this:

• Set 'allow-newer: true' in /home/travis/.stack/config.yaml to ignore all version constraints and build anyway.

• Recommended action: try adding the following to your extra-deps in /home/travis/build/ocramz/heidi/stack.yaml:

• hashable-time-0.3@sha256:41a484892d585f206b865f94dc2dd9e2d8fdcce08acc3a91ebea56774395249b,1157

[AR2202]

Thanks @ocramz for your explanation.
I lowered the lower bound for the hashable-time version, which means it now builds with all the resolvers except 12.26.
As far as I understand, 12.26 doesn't have any version of hashable-time. The suggestion is to add it to the extra-deps in the stack.yaml file, but this leads to a lot of other packages being incompatible, and I guess adding lots of extra-deps to the stack.yaml file isn't the correct solution.
Do you have any suggestions?