feature: flags to control the output

[codesenberg]

In a setup where bombardier is used by some script it is quite inconvenient to parse bombardier's output as it turned out (see #24). As a first step to resolve this issue, I plan to add two flags: --print (short: -p) and --no-print. The first one will control what to print in case something needs to be printed. Syntax will look something like:

--print=[<value>,]{1,2}<value>
<value> = intro (i) | progress (p) | result (r)

Some examples:

# prints intro, progress and result
bombardier --print=r,i,p <url>
# same as above
bombardier --print=intro,progress,result <url>
# result only
bombardier --print=r <url>
# same as above
bombardier -p=result <url>

In case you don't need any output, you will be able to use --no-print flag.