Quickstart:
----------

First time mining verthash or don't have a Verthash data file:

--algo verthash --verify --url ...

Verthash data file already exists:

--algo verthash --data-file /path/to/verthash.dat --url ...


Background:
----------

Verthash algorithm requires a data file for hashing. This file is
static, portable, and only needs to be created once.

A Verthash data file created by VerthashMiner can also be used by cpuminer-opt
and used simultaneously by both miners.

Due to its size >1GB it is recommened one data file be created and
stored in a permanent location accessible to any miner that wants to use it.

New command line options:
------------------------

cpuminer-opt adds two new command line options for verthash. The names
and some behaviour is changed from VerthashMiner.

--data-file /path/to/verthash.dat
  default when not used is verthash.dat in current working directory.  

--verify
  verify integrity of file specified by --data-file, or if not specified
  the default data file if it exists, or create a default file and verify it
  if one does not yet exist. Data file verification is disabled by default.

Detailed usage:
--------------

If a data file already exists it can be selected using the --data-file
option to specify the path and name of the file.

--algo verthash --datafile /path/to/verthash.dat --url ...

If the --data-file option is not used the default is to use 'verthash.dat'
from the current working directory.

If no data file exists it can be created by using the --verify option
without the --data-file option. If the default data file is not found in
the current directory it will be created.

--algo verthash --verify --url ...

Data file creation can take up to 30 minutes on a spinning hard drive. 
Once created the new data file will be verified and used immediately
if a valid url and user were included on the command line.

A default data file can be created by ommitting the url option. That will
either verify an existing default data file or create one and verify it,
then exit.

--algo verthash --verify

A data file will never be created if --data-file is specified. The miner
will exit with an error if the file is not found. This is to avoid accidentally
creating an unwanted data file due to a typo.

After creation the data file can moved to a more convenient location and
referenced by --data-file, or left where it is and used by default without the
--data-file option.

Data file verification takes a few seconds and is disabled by default.
VerthashMiner enables data file verification by default and has an option to
disable it.

The --verify option is intended primarily to create a new file. It's 
not necessary or useful to verify a file every time the miner is started.