Added symbol vert offset argument

[AckslD]

I find the symbols not really centered vertically so added an argument to shift them (while leaving the text as it is). Defaults to 0 (no change). A value of 2 works nice for me.

[t-wissmann]

But this only works for a personally patched version of lemonbar by you, doesn't it?

[AckslD]

@t-wissmann As mentioned in #10, it seems this maybe only works with lemonbar-xft

[t-wissmann]

Then I suggest that you set the default value

symbol_vert_offset=None

and only add the -o-flags if symbol_vert_offset is not None, for example:

if symbol_vert_offset is not None:
    command += [ '-o -%d' % symbol_vert_offset ]

Also, you can add a comment that setting symbol_vert_offset only works for lemonbar-xft and I think then it works for every branch of lemonbar :-)

[AckslD]

Sounds good @t-wissmann! I changed to only use that flag if symbol_vert_offset is set. I added a comment next to the argument of the method.

[t-wissmann]

Great, thanks!