getting_started/4: fix "like the variable" typo, corrected was_accessed?().¹

1: was_accessed?() was actually was_not_accessed?(); I inverted the return
values for all declarations provided.
getting_started/3: changed "last call optimiation" to "tail call optimization".
getting_started/4: fix "data structured" typo.
getting_started/4: 4.2: reword head of 2nd paragraph.¹

1: I find this difficult to express in a clear manner.
getting_started/4: 4.2 - 4.2.3: reword sentences, tidy flow, correct IEx output, codify more syntax.
getting_started/4: 4.3: rewrite & reflow bits and pieces.¹

1: I got carried away, but tried to avoid changing the meaning of anything.
This is an area that still needs some work, but I'm not going to dig my boots
in.
getting_started/6: 6.5: correct call in func equivalent, codify `&1`.
getting_started/6: 6.5: strike "around" at end of 2nd-to-last paragraph.
getting_started/6: 6.5: reword last sentence in last paragraph, tidy.
Merge pull request #143 from komiga/gs-4-tidy

Fix typos, codify syntax, reword & reflow sentences in Getting Started sections 4.2 - 4.2.3
Merge pull request #144 from komiga/gs-4-exception-rewrite

Rewrite & reflow majority of Getting Started section 4.3
Merge pull request #145 from komiga/gs-6-tidy

Correct examples and reword a few things in Getting Started section 6.5
Merge pull request #140 from komiga/master

Fix typos and normalize syntax highlighting in chapters 1, 2, and 3 of Getting Started
Merge pull request #142 from komiga/gs-tail-call

Changed "last call optimiation" to "tail call optimization" in Getting Started chapter 3
Merge pull request #141 from komiga/file-access

Fix typo and corrected FileAccess.was_accessed?() return value in Getting Started chapter 4
Make a distinction in between true and `true`