Add a helper for skipping input stream data

[WickedShell]

I find it quite useful to be able to skip all buffered input data on a port, and have been doing this externally to clj-serial, but it makes a lot of sense as a helper function, especially since clj-serial already has to perform this action.

[WickedShell]

Travis fails due to:

Exception in thread "main" java.lang.UnsupportedClassVersionError: purejavacomm/CommPortIdentifier : Unsupported major.minor version 52.0, compiling:(serial/core.clj:1:1)

Test suite passes here, on:

openjdk version "1.8.0_121"
OpenJDK Runtime Environment (build 1.8.0_121-b13)
OpenJDK 64-Bit Server VM (build 25.121-b13, mixed mode)

Not sure what the deal is with the java versions in Travis, but I haven't noticed any problem with purejavacomm and versions...

[peterschwarz]

That is strange. I will have to look into that...

[WickedShell]

@peterschwarz I spent some time debugging this, at somepoint someone decided to rerelease purejavacomm 1.0.0. and they recompiled it for Java 8, while the previous ones were all compiled for Java 5. It works locally on my machine as I have a cached version of purejavacomm that is compiled for Java 5. Short of convincing purejavacomm to release a different targeted version we would need to build it ourselves as a submodule.

I've commented on the open issue they have related to this, and will post back if they come up with anything useful nyholku/purejavacomm#99

Unfortunately this means anyone not running on Java 8 won't be able to build clj-serial in the future, and we are stuck on updating to their latest release (of which there have been 2 small ones that clj-serial is dragging behind).

Edit: In fact if you were to kick of a travis job on master you would see it fail at this point

[WickedShell]

@peterschwarz PureJavaComm fixed the Javca compilation target issue in the 1.0.1 release, if we update to that (which we should anyways), then there are no longer any CI issues with this. I'll rebase my other PR ontop of this if you are happy with the proposed changes.

[peterschwarz]

Looks good. Thanks for the efforts.