Given markdown;
# a

## b

### c

#### d

##### e

Execute (HeaderIncrease without forbidden level):
  :HeaderIncrease

Expect (increase level of all headers):
  ## a

  ### b

  #### c

  ##### d

  ###### e

Given markdown;
# a

###### b

Execute (HeaderIncrease with forbidden level):
  :HeaderIncrease

Expect (no changes):
  # a

  ###### b

Given markdown;
## a

### b

#### c

##### d

###### e

Execute (HeaderDecrease without forbidden level):
  :HeaderDecrease

Expect (decrease level of all headers):
  # a

  ## b

  ### c

  #### d

  ##### e

Given markdown;
# a

## b

### c

#### d

##### e

###### f

Execute (HeaderDecrease with forbidden level):
  :HeaderDecrease

Expect (no changes):
  # a

  ## b

  ### c

  #### d

  ##### e

  ###### f

Given markdown;
a
=

b
-

Execute (HeaderIncrease with setext headers):
  :HeaderIncrease

Expect (convert to atx headers):
  ## a

  ### b

Given markdown;
a
-

Execute (HeaderDecrease with setext headers):
  :HeaderDecrease

Expect (convert to atx headers):
  # a