fix: add read buffer collection option

[LaurenceLiZhixin]

What this PR does: Create an option to let user define if the session would collect read buffer.

if s.readBufferCollectionOpen {
        pktBuf = gxbytes.GetBytesBuffer()
    } else {
        pktBuf = new(bytes.Buffer)
    }

    defer func() {
        gxbytes.PutBytes(bufp)
        if s.readBufferCollectionOpen {
            gxbytes.PutBytesBuffer(pktBuf)
        }
    }()

Consider the case for TCP conn that sometimes pass large data. If the large Buffer is collected, other TCP conn will be polluted, resulting in large buffers received by other TCP coon, and take up a large scale of memeory.

[codecov-commenter]

Codecov Report

Merging #75 (cb1b367) into master (917228c) will increase coverage by 0.20%. The diff coverage is 91.30%.

@@            Coverage Diff             @@
##           master      #75      +/-   ##
==========================================
+ Coverage   69.14%   69.34%   +0.20%     
==========================================
  Files           8        8              
  Lines        1426     1442      +16     
==========================================
+ Hits          986     1000      +14     
- Misses        347      348       +1     
- Partials       93       94       +1     

Impacted Files	Coverage Δ
session.go	70.10% <81.81%> (-0.18%)	:arrow_down:
client.go	71.86% <100.00%> (+0.32%)	:arrow_up:
options.go	83.01% <100.00%> (+2.16%)	:arrow_up:
server.go	68.23% <100.00%> (+0.34%)	:arrow_up:

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