feat: added support for setting context variables

Added ability to specify "context variables", which can be used to
render script files from a template. For example, the user could write

mkdir %semester%-%year%

in their script file and specify

--context-variable="'semester'='Spring'" --context-variable="'year'='2019'"

on the command line to have

mkdir Spring-2019

show up during the session.

This is useful for running commands that depend on the date. For
example, while teaching a class.

dropped cmake version 3.1 requirement to 2.8 in testing directory.

fixed compile error for builds without libxdo.

Added keysym mode

In keysym mode, keysym codes are read from the script file and emitted
using libxdo. This allows key logging tools that display
which keys are being pressed to work (like screenkey)

added --test option for testing scripts

fixed bug in passthrough mode

for some reason passing return characters (10) to terminal does not
work in some cases. First noticed when trying to automate the nano text
editor. Changing returns to carriage returns (13) seems to fix it, so
now passthrough mode sends a '\r' if a return is received.

switched to boost regex library to support escaping hashtags (needed …

…negative lookup capabilities)

fixed bug in dirname function

added support for including scripts.

removed command and post-command options. added pause before exit.

removed the pre and post command options since setup and cleanup options
to this now.

added a pause after the script has been ran to keep the shell from
exiting before output of last command is displayed.