Add Donate button about il-repack

[dzmitry-lahoda]

If you want to avoid donation consider redirect it to some FOSS project or organization protecting freedom, or whatever. https://github.com/asd-and-Rizzo/asd-and-Rizzo.github.io/blob/master/how-to-avoid-donations.md

[gluck]

Words of usefulness are thanks enough, how about a statement like the below ?

If you like this tool and want to express your thanks, you can contribute either time to the project (issue triage or pull-requests) or donate money to the Free Software Foundation.

[dzmitry-lahoda]

Good for readme, also may add link to fsf page.

Some ideas for possible features which may or may be done during IL merge dotnet/roslyn#98 see Componentization. Seems some of these are elaborated somewhere else.

Also would be interesting to eliminate not used code during merge into exe(may get rid of not used public cause exe is not for reference), with some definition about reflection safety.