Change postfix Katakana conversion to take characters while hiragana continues.

* scm/tutcode.scm
  - (tutcode-begin-postfix-katakana-conversion):
    If yomi-len argument is zero, take characters while hiragana continues.
    For negative value, treat absolute value as excluding characters count.
Change postfix Katakana conversion to acquire middle dot as target hiragana.

* scm/tutcode.scm
  - (tutcode-begin-postfix-katakana-conversion):
    Change not to convert to Katakana if acquired length is shorter
    than specified negative yomi count.
    Change to use tutcode-postfix-katakana-acquire-yomi.
  - (tutcode-postfix-katakana-acquire-yomi):
    New function to acquire characters while hiragana continues.
  - (tutcode-hiragana?): New function.
Change acquiring yomi of postfix katakana conversion to be customizable.

* scm/tutcode.scm
  - (tutcode-postfix-katakana-char-list): New variable.
  - (tutcode-begin-postfix-katakana-conversion):
    Change to call tutcode-postfix-katakana-acquire-char?
  - (tutcode-postfix-katakana-acquire-char?):
    New function extracted from tutcode-begin-postfix-katakana-conversion.
Add function to shrink katakana string just after postfix katakana conversion.

* scm/tutcode.scm
  - (tutcode-postfix-katakana-shrink): New function.
Fix to consider katakana mode on postfix katakana conversion.
(regression by recent change at eed594c)

* scm/tutcode.scm
  - (tutcode-postfix-katakana-shrink): Consider current katakana mode.
  - (tutcode-postfix-katakana-acquire-yomi):
    Follow argument addition of tutcode-postfix-katakana-acquire-char?
  - (tutcode-postfix-katakana-acquire-char?):
    Consider current katakana mode.
  - (tutcode-katakana?): New function.
Add key customs for postfix katakana conversion with exclude or shrink.

* scm/tutcode-key-custom.scm
  - (tutcode-postfix-katakana-0-start-sequence,
     tutcode-postfix-katakana-exclude-1-sequence,
     tutcode-postfix-katakana-exclude-2-sequence,
     tutcode-postfix-katakana-exclude-3-sequence,
     tutcode-postfix-katakana-exclude-4-sequence,
     tutcode-postfix-katakana-exclude-5-sequence,
     tutcode-postfix-katakana-exclude-6-sequence,
     tutcode-postfix-katakana-shrink-1-sequence,
     tutcode-postfix-katakana-shrink-2-sequence,
     tutcode-postfix-katakana-shrink-3-sequence,
     tutcode-postfix-katakana-shrink-4-sequence,
     tutcode-postfix-katakana-shrink-5-sequence,
     tutcode-postfix-katakana-shrink-6-sequence): New key custom.
* scm/tutcode.scm
  - (tutcode-stroke-help-update-alist-with-rule):
    Add labels for new custom keys.
  - (tutcode-proc-state-on):
    Add check of new custom keys.
  - (tutcode-custom-set-mazegaki/bushu-start-sequence!):
    Support new custom keys.
Add a section for 1.8.4.

* NEWS
  - (Overview of changes from 1.8.3 to 1.8.4): New section.
Add NEWS about uim-tutcode.

* NEWS
  - (Overview of changes from 1.8.3 to 1.8.4):
    Add Enhancements about uim-tutcode.
Remove empty subsections from NEWS.

* NEWS
  - (Overview of changes from 1.8.3 to 1.8.4):
    Remove empty subections Fixes and Others.
Update RELNOTE.

* RELNOTE
  - Update from 1.8.3 to 1.8.4.
Update RELEASING.

* doc/RELEASING
  - Replace the argument of git-clone.