Remove logrus dependency, and add functional options to specify logger

[kenshaw]

This changeset removes the non-standard dependency to logrus, leaving
the only dependencies used in ansiterm and winterm as Go standard lib
packages. This also has the added benefit of removing a superfulous
package level variable (logger) in both ansiterm and winterm.

The changes made here introduce a backwards compatible change to the
API signatures of ansiterm.CreateParser and winterm.CreateWinEventHandler
by introducing the optional functional parameters pattern on both.
Additionally, both ansiterm and winterm packages receive a WithLogf()
func to specify a logging func to use, which can be passed a func
with the standard Printf signature, ie: func(string, ...interface{}).

This maintains the existing behavior of checking for the environment
variable DEBUG_TERMINAL, and writing to the files ansiParser.log and
winEventHandler.log. For ansiterm/winterm, if a logging func has been
specified as well as having DEBUG_TERMINAL set, then both the respective
*.log file and the passed logging func will receive the data.

Note: for simplicity purposes, the single instance in ansiterm where
there was a "warning" and "error" was logged has been changed to use the
single log, but the messages have been prefixed with WARNING and ERROR
respectively. This was done entirely for simplicity reasons.
Additionally 2 other logging calls have been removed where it was
prudent to do so, and one other logging line was moved to a different
location in order to avoid changing some utility funcs.

[kenshaw]

I'm confused about the activity from the msftclas and msftgits bots? It removed the cla-signed tag. Does that imply this has no chance of being merged? In anticipation of submitting this PR, I had signed the DocuSign document ahead of time.

Any clarification would be appreciated. Thanks!

[msftclas]

@kenshaw, thanks for signing the contribution license agreement. We will now validate the agreement and then the pull request.

Thanks, Microsoft Pull Request Bot

[jstarks]

Thanks for the contribution. Looks good.

[kenshaw]

Thank you, much appreciated!