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Re-structure list of breaking changes.

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@ -3,33 +3,43 @@ Solidity v0.8.0 Breaking Changes
********************************
This section highlights the main breaking changes introduced in Solidity
version 0.8.0, along with the reasoning behind the changes and how to update
affected code.
version 0.8.0.
For the full list check
`the release changelog <https://github.com/ethereum/solidity/releases/tag/v0.8.0>`_.
Semantic and Syntactic Changes
==============================
Silent Changes of the Semantics
===============================
This section lists changes where you have to modify your code
and it does something else afterwards.
This section lists changes where existing code changes its behaviour without
the compiler notifying you about it.
* Arithmetic operations revert on underflow and overflow. You can use ``unchecked { ... }`` to use
the previous wrapping behaviour.
Checks for overflow are very common, so we made them the default to increase readability of code,
even if it comes at a slight increase of gas costs.
* Explicit conversions from negative literals and literals larger than ``type(uint160).max`` to ``address`` are now disallowed.
* Exponentiation is right associative, i.e., the expression ``a**b**c`` is parsed as ``a**(b**c)``.
Before 0.8.0, it was parsed as ``(a**b)**c``.
Semantic only Changes
=====================
This is the common way to parse the exponentiation operator.
* Failing assertions (and other internal checks like division by zero) do not use the invalid opcode anymore but instead revert
with error data equal to a function call to ``Panic(uint256)`` with an error code specific to the circumstances.
* Failing assertions and other internal checks like division by zero or arithmetic overflow do
not use the invalid opcode but instead the revert opcode.
More specifically, they will use error data equal to a function call to ``Panic(uint256)`` with an error code specific
to the circumstances.
This will save gas on errors while it still allows static analysis tools to detect these situations.
This will save gas on errors while it still allows static analysis tools to distinguish
these situations from a revert on invalid input, like a failing ``require``.
New Restrictions
================
Syntactic Only Changes
======================
* Explicit conversions from negative literals and literals larger
than ``type(uint160).max`` to ``address`` are disallowed.
The previous behaviour was likely ambiguous.
* The global functions ``log0``, ``log1``, ``log2``, ``log3`` and ``log4`` have been removed.
These are low-level functions that were largely unused. Their behaviour can be accessed from inline assembly.
These are low-level functions that were largely unused. Their behaviour can be accessed from inline assembly.