Modify to get constant of parent module in singleton class; fix #3568

The resulting behavior is different from CRuby, but modifying
hash key afterwards is undefined behavior in ISO spec.

Modify class variable definition in singleton class; fix #3539

Fix Enumerator#each_with_index with block

In previous version,

```
a = [3, 2, 1]
e = a.each
e.sort_by(&:to_i) # => []
```

In this version,

```
a = [3, 2, 1]
e = a.each
e.sort_by(&:to_i) # => [1, 2, 3]
```

Should raise FloatDomainError

Renumber hash keys during dup since there may be duplicates.

Set proper class to subclass of Array

More compatibility to CRuby.

Implement Array#slice!

Fix infinity loop ref #3546

And some cases should raise FloatDomainError

Fix lost lineno

Ignore file generated by ctags

Hash sub class creates new sub class objects instead of Hash

Fix result if pattern is empty

Update String#gsub and String#gsub!

916b8e let code executed with mrb->exc set, and may cause a crash
like #3519. Instead modified OP_RESCUE again. To retrieve the exception
object, we use `OP_RESCUE R(A), 0, 0` (old behavior). To compare the
exception object and the class, we use `OP_RESCUE R(A), R(B), 1`.

The reason we use OP_RESCUE for two instruction switched by operand
C is to save the instruction space.

As a result, the following code:
```ruby
begin
  raise "a"
rescue TypeError
  p 1
rescue RuntimeError
  p 2
end
```
will be compiled as:
```
irep 0x55cd1f565cb0 nregs=4 nlocals=1 pools=1 syms=4 reps=0
file: -
    2 000 OP_ONERR	005
    2 001 OP_LOADSELF	R1
    2 002 OP_STRING	R2	L(0)	; "a"
    2 003 OP_SEND	R1	:raise	1
    2 004 OP_JMP	023
    2 005 OP_RESCUE	R1
    3 006 OP_GETCONST	R2	:TypeError
    3 007 OP_RESCUE	R1	R2	cont
    3 008 OP_JMPIF	R2	010
    3 009 OP_JMP	014
    4 010 OP_LOADSELF	R1
    4 011 OP_LOADI	R2	1
    4 012 OP_SEND	R1	:p	1
    4 013 OP_JMP	024
    5 014 OP_GETCONST	R2	:RuntimeError
    5 015 OP_RESCUE	R1	R2	cont
    5 016 OP_JMPIF	R2	018
    5 017 OP_JMP	022
    6 018 OP_LOADSELF	R1
    6 019 OP_LOADI	R2	2
    6 020 OP_SEND	R1	:p	1
    6 021 OP_JMP	024
    6 022 OP_RAISE	R1
    6 023 OP_POPERR	1
    6 024 OP_STOP
```