Add support for different length up and down error bars

This patch utilizes new features in pgfplots 1.9 that allow
different length of up and down errorbars.  The coordinate
input format changes from:
  (1,21.35) +-= (0.0,8.65)
to (for example):
  (1,21.35) += (0.0,8.65) -= (0.0,10.32)

To be honest I'm not exactly sure if this patch has any side-
effects, due to lack of time it hasn't been properly tested,
but works for my application, which is a matlab plot generated
by the command:
  errorbar(X, Y, ED, EU)
where X, Y, ED and EU are simple vectors.
fileHandleValidation: only one argument

This function is used once, where it takes one argument.
It actually only uses one argument
isCellOrChar: only one argument

inputParser uses a one-argument validation function,
and the second argument was not used
validation functions: help string shortened
m2t.cmdOpts -> ipp at the beginning

This cleans up the code quite a bit and makes typos less likely
Cleaned up input parser

A lot of entries had a single line of comment that stated the same
as the parameter name OR even had wrong information.
Since 99% of this information is already contained in the HELP text,
this reduces the redundant information.
Merge pull request #288 from egeerardyn/cleanup-input-parsing

Cleanup input parsing
Merge pull request #266 from karih/master

Add support for different length up and down error bars
add unit test for asymmetric error bars
added a newline in the error bar output
update changelog for 0.4.4