refactor(parser): merge 'LiteralParagraph' and 'Paragraph' rules

[xcoulon]

Also, removed obsolete constants for attributes.
Also, remove support for implicit continuation of
literal paragraph: + character is required.

[codecov]

Codecov Report

Merging #1032 (413f7cd) into master (113f625) will increase coverage by 0.06%.
The diff coverage is 91.57%.

@@            Coverage Diff             @@
##           master    #1032      +/-   ##
==========================================
+ Coverage   80.23%   80.29%   +0.06%     
==========================================
  Files          86       86              
  Lines        7017     7019       +2     
==========================================
+ Hits         5630     5636       +6     
+ Misses        866      861       -5     
- Partials      521      522       +1     

[github-actions]

Comparing with master branch:

name                                          old time/op    new time/op    delta
RealDocumentProcessing/demo.adoc-2              20.9ms ± 4%    20.6ms ± 2%    ~     (p=0.063 n=9+9)
RealDocumentProcessing/vertx-examples.adoc-2    65.7ms ± 5%    61.6ms ± 5%  -6.19%  (p=0.000 n=9+10)
RealDocumentProcessing/mocking.adoc-2           58.2ms ± 4%    56.3ms ± 4%  -3.15%  (p=0.003 n=10+10)

name                                          old alloc/op   new alloc/op   delta
RealDocumentProcessing/demo.adoc-2              9.29MB ± 0%    9.29MB ± 0%  +0.00%  (p=0.010 n=10+9)
RealDocumentProcessing/vertx-examples.adoc-2    25.9MB ± 0%    25.9MB ± 0%  +0.00%  (p=0.034 n=8+10)
RealDocumentProcessing/mocking.adoc-2           21.7MB ± 0%    21.7MB ± 0%  -0.00%  (p=0.036 n=9+8)

name                                          old allocs/op  new allocs/op  delta
RealDocumentProcessing/demo.adoc-2                112k ± 0%      112k ± 0%    ~     (all equal)
RealDocumentProcessing/vertx-examples.adoc-2      329k ± 0%      329k ± 0%    ~     (p=0.222 n=10+10)
RealDocumentProcessing/mocking.adoc-2             328k ± 0%      328k ± 0%    ~     (p=0.136 n=10+10)

Comparing with latest release:

name                                          old time/op    new time/op    delta
RealDocumentProcessing/demo.adoc-2              20.9ms ± 4%    19.3ms ± 3%   -7.31%  (p=0.000 n=9+9)
RealDocumentProcessing/vertx-examples.adoc-2    65.7ms ± 5%    56.3ms ± 4%  -14.39%  (p=0.000 n=9+10)
RealDocumentProcessing/mocking.adoc-2           58.2ms ± 4%    54.7ms ± 3%   -5.95%  (p=0.000 n=10+10)

name                                          old alloc/op   new alloc/op   delta
RealDocumentProcessing/demo.adoc-2              9.29MB ± 0%    8.85MB ± 0%   -4.72%  (p=0.000 n=10+10)
RealDocumentProcessing/vertx-examples.adoc-2    25.9MB ± 0%    24.0MB ± 0%   -7.47%  (p=0.000 n=8+10)
RealDocumentProcessing/mocking.adoc-2           21.7MB ± 0%    21.6MB ± 0%   -0.57%  (p=0.000 n=9+9)

name                                          old allocs/op  new allocs/op  delta
RealDocumentProcessing/demo.adoc-2                112k ± 0%      106k ± 0%   -5.06%  (p=0.001 n=7+7)
RealDocumentProcessing/vertx-examples.adoc-2      329k ± 0%      305k ± 0%   -7.33%  (p=0.000 n=10+10)
RealDocumentProcessing/mocking.adoc-2             328k ± 0%      326k ± 0%   -0.56%  (p=0.000 n=10+9)