version 3.0 - Introducing iematch and latex to iebaltab

New command: iematch
iematch matches observations in one group to observations in another group based on one continuous variable. Used to, for example, identify individual counterfactual observations to a sample of treatment observations. Allows for both one-to-one matches and many-to-one matches.

New major feature: latex support in iebaltab
@luizaandrade implemented the option to output the balance tables in latex. Fixes issue #5

Minor updates:
This version also included fixes for issues: #9 , #10 and #15