added internal tempering in grem with example

# LJ particles

variable        lambda world 400 410 420 430

variable        rep world 1 2 3 4

#variable        walker world 1 2 3 4

variable        T0 equal 300.0

variable        press equal 0.0

units           real

atom_style      full

pair_style      lj/cut 5.0

read_data       "lj.data"

thermo          10

thermo_style    custom step temp pe etotal press vol

timestep        1.0

fix             fxnpt all npt temp ${T0} ${T0} 1000.0 iso ${press} ${press} 10000.0 

fix             fxgREM all grem ${lambda} -.01 -30000 fxnpt

thermo_modify   press fxgREM_press

grem            100000 1000 ${lambda} fxgREM fxnpt 10294 98392 

#write_data      lj-out.data