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 in the specified location.
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.