title: Bump version of project with custom keyword in front
body: <p>I have installed <code>bump2version</code> and my <code>.bumpversion.cfg</code> file is having following contents:</p>
  <pre><code>[bumpversion]
  current_version = 0.1.11
  commit = False
  tag = True
  parse = (?P&lt;major&gt;\d+)\.(?P&lt;minor&gt;\d+)\.(?P&lt;patch&gt;\d+)(\-(?P&lt;release&gt;[a-z]+)(?P&lt;build&gt;\d+))?
  serialize = 
      {major}.{minor}.{patch}
      {major}.{minor}.{patch}
  
  [bumpversion:part:release]
  optional_value = prod
  first_value = dev
  values = 
      dev
      prod
  
  [bumpversion:part:build]
  
  [bumpversion:file:VERSION]
  search = version: {current_version}
  replace = version: {new_version}
  </code></pre>
  <p>There is also a version file named <code>VERSION</code> having below content:</p>
  <pre><code>version: 0.1.11
  </code></pre>
  <p>When I run <code>bumpversion patch</code>, it updates things properly. The only issue is instead of
  <code>0.1.11</code>, i actually want additional v in it i.e.<code>v0.1.11</code></p>
  <p>I tried to implement it in following way</p>
  <pre><code>[bumpversion]
  current_version = v0.1.11
  commit = False
  tag = True
  parse = (?P&lt;key&gt;\d+)(?P&lt;major&gt;\d+)\.(?P&lt;minor&gt;\d+)\.(?P&lt;patch&gt;\d+)(\-(?P&lt;release&gt;[a-z]+)(?P&lt;build&gt;\d+))?
  serialize = 
      {major}.{minor}.{patch}
      {major}.{minor}.{patch}
  
  [bumpversion:part:release]
  optional_value = prod
  first_value = dev
  values = 
      dev
      prod
  
  [bumpversion:part:key]
  optional_value = v
  first_value = v
  values = 
      v
  
  [bumpversion:part:build]
  
  [bumpversion:file:VERSION]
  search = version: {current_version}
  replace = version: {new_version}
  </code></pre>
  <p>Also replaced the contents of file <code>VERSION</code> in following way:</p>
  <pre><code>version: v0.1.11
  </code></pre>
  <p>But this implementation gives following issue on running <code>bumpversion patch</code>:</p>
  <pre><code>bumpversion patch
  Evaluating 'parse' option: '(?P&lt;key&gt;\d+)(?P&lt;major&gt;\d+)\.(?P&lt;minor&gt;\d+)\.(?P&lt;patch&gt;\d+)(\-(?P&lt;release&gt;[a-z]+)(?P&lt;build&gt;\d+))?' does not parse current version 'v0.1.11'
  usage: bumpversion [-h] [--config-file FILE] [--verbose] [--list] [--allow-dirty] [--parse REGEX] [--serialize FORMAT] [--search SEARCH]
                     [--replace REPLACE] [--current-version VERSION] [--no-configured-files] [--dry-run] --new-version VERSION [--commit | --no-commit]    
                     [--tag | --no-tag] [--sign-tags | --no-sign-tags] [--tag-name TAG_NAME] [--tag-message TAG_MESSAGE] [--message COMMIT_MSG]
                     [--commit-args COMMIT_ARGS]
                     part [file ...]
  bumpversion: error: the following arguments are required: --new-version
  </code></pre>
  <p>Can someone help me as to how i can modify parse so that it an be parsed correctly.</p>
  <p>Thanks in advance..</p>